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Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Browse source 
Pull locking updates from Ingo Molnar:
 "The main changes in this cycle are:

   - big rtmutex and futex cleanup and robustification from Thomas
     Gleixner
   - mutex optimizations and refinements from Jason Low
   - arch_mutex_cpu_relax() removal and related cleanups
   - smaller lockdep tweaks"

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (23 commits)
  arch, locking: Ciao arch_mutex_cpu_relax()
  locking/lockdep: Only ask for /proc/lock_stat output when available
  locking/mutexes: Optimize mutex trylock slowpath
  locking/mutexes: Try to acquire mutex only if it is unlocked
  locking/mutexes: Delete the MUTEX_SHOW_NO_WAITER macro
  locking/mutexes: Correct documentation on mutex optimistic spinning
  rtmutex: Make the rtmutex tester depend on BROKEN
  futex: Simplify futex_lock_pi_atomic() and make it more robust
  futex: Split out the first waiter attachment from lookup_pi_state()
  futex: Split out the waiter check from lookup_pi_state()
  futex: Use futex_top_waiter() in lookup_pi_state()
  futex: Make unlock_pi more robust
  rtmutex: Avoid pointless requeueing in the deadlock detection chain walk
  rtmutex: Cleanup deadlock detector debug logic
  rtmutex: Confine deadlock logic to futex
  rtmutex: Simplify remove_waiter()
  rtmutex: Document pi chain walk
  rtmutex: Clarify the boost/deboost part
  rtmutex: No need to keep task ref for lock owner check
  rtmutex: Simplify and document try_to_take_rtmutex()
  ...
This commit is contained in:
Linus Torvalds 2014-08-04 16:09:06 -07:00
commit 8efb90cf1e
48 changed files with 718 additions and 436 deletions
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1
arch/alpha/include/asm/processor.h
View file

@ -57,6 +57,7 @@ unsigned long get_wchan(struct task_struct *p);
((tsk) == current ? rdusp() : task_thread_info(tsk)->pcb.usp)
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
#define ARCH_HAS_PREFETCH
#define ARCH_HAS_PREFETCHW

2
arch/arc/include/asm/processor.h
View file

@ -62,6 +62,8 @@ unsigned long thread_saved_pc(struct task_struct *t);
#define cpu_relax() do { } while (0)
#endif
#define cpu_relax_lowlatency() cpu_relax()
#define copy_segments(tsk, mm) do { } while (0)
#define release_segments(mm) do { } while (0)

2
arch/arm/include/asm/processor.h
View file

@ -82,6 +82,8 @@ unsigned long get_wchan(struct task_struct *p);
#define cpu_relax() barrier()
#endif
#define cpu_relax_lowlatency() cpu_relax()
#define task_pt_regs(p) \
((struct pt_regs *)(THREAD_START_SP + task_stack_page(p)) - 1)

1
arch/arm64/include/asm/processor.h
View file

@ -129,6 +129,7 @@ extern void release_thread(struct task_struct *);
unsigned long get_wchan(struct task_struct *p);
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
/* Thread switching */
extern struct task_struct *cpu_switch_to(struct task_struct *prev,

1
arch/avr32/include/asm/processor.h
View file

@ -92,6 +92,7 @@ extern struct avr32_cpuinfo boot_cpu_data;
#define TASK_UNMAPPED_BASE (PAGE_ALIGN(TASK_SIZE / 3))
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
#define cpu_sync_pipeline() asm volatile("sub pc, -2" : : : "memory")
struct cpu_context {

2
arch/blackfin/include/asm/processor.h
View file

@ -99,7 +99,7 @@ unsigned long get_wchan(struct task_struct *p);
#define KSTK_ESP(tsk) ((tsk) == current ? rdusp() : (tsk)->thread.usp)
#define cpu_relax() smp_mb()
#define cpu_relax_lowlatency() cpu_relax()
/* Get the Silicon Revision of the chip */
static inline uint32_t __pure bfin_revid(void)

1
arch/c6x/include/asm/processor.h
View file

@ -121,6 +121,7 @@ extern unsigned long get_wchan(struct task_struct *p);
#define KSTK_ESP(task) (task_pt_regs(task)->sp)
#define cpu_relax() do { } while (0)
#define cpu_relax_lowlatency() cpu_relax()
extern const struct seq_operations cpuinfo_op;

1
arch/cris/include/asm/processor.h
View file

@ -63,6 +63,7 @@ static inline void release_thread(struct task_struct *dead_task)
#define init_stack (init_thread_union.stack)
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
void default_idle(void);

1
arch/hexagon/include/asm/processor.h
View file

@ -56,6 +56,7 @@ struct thread_struct {
}
#define cpu_relax() __vmyield()
#define cpu_relax_lowlatency() cpu_relax()
/*
* Decides where the kernel will search for a free chunk of vm space during

1
arch/ia64/include/asm/processor.h
View file

@ -548,6 +548,7 @@ ia64_eoi (void)
}
#define cpu_relax() ia64_hint(ia64_hint_pause)
#define cpu_relax_lowlatency() cpu_relax()
static inline int
ia64_get_irr(unsigned int vector)

1
arch/m32r/include/asm/processor.h
View file

@ -133,5 +133,6 @@ unsigned long get_wchan(struct task_struct *p);
#define KSTK_ESP(tsk) ((tsk)->thread.sp)
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
#endif /* _ASM_M32R_PROCESSOR_H */

1
arch/m68k/include/asm/processor.h
View file

@ -176,5 +176,6 @@ unsigned long get_wchan(struct task_struct *p);
#define task_pt_regs(tsk) ((struct pt_regs *) ((tsk)->thread.esp0))
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
#endif

1
arch/metag/include/asm/processor.h
View file

@ -155,6 +155,7 @@ unsigned long get_wchan(struct task_struct *p);
#define user_stack_pointer(regs) ((regs)->ctx.AX[0].U0)
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
extern void setup_priv(void);

1
arch/microblaze/include/asm/processor.h
View file

@ -22,6 +22,7 @@
extern const struct seq_operations cpuinfo_op;
# define cpu_relax() barrier()
# define cpu_relax_lowlatency() cpu_relax()
#define task_pt_regs(tsk) \
(((struct pt_regs *)(THREAD_SIZE + task_stack_page(tsk))) - 1)

1
arch/mips/include/asm/processor.h
View file

@ -367,6 +367,7 @@ unsigned long get_wchan(struct task_struct *p);
#define KSTK_STATUS(tsk) (task_pt_regs(tsk)->cp0_status)
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
/*
* Return_address is a replacement for __builtin_return_address(count)

2
arch/mn10300/include/asm/processor.h
View file

@ -68,7 +68,9 @@ extern struct mn10300_cpuinfo cpu_data[];
extern void identify_cpu(struct mn10300_cpuinfo *);
extern void print_cpu_info(struct mn10300_cpuinfo *);
extern void dodgy_tsc(void);
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
/*
* User space process size: 1.75GB (default).

1
arch/openrisc/include/asm/processor.h
View file

@ -101,6 +101,7 @@ extern unsigned long thread_saved_pc(struct task_struct *t);
#define init_stack (init_thread_union.stack)
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
#endif /* __ASSEMBLY__ */
#endif /* __ASM_OPENRISC_PROCESSOR_H */

1
arch/parisc/include/asm/processor.h
View file

@ -338,6 +338,7 @@ extern unsigned long get_wchan(struct task_struct *p);
#define KSTK_ESP(tsk) ((tsk)->thread.regs.gr[30])
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
/* Used as a macro to identify the combined VIPT/PIPT cached
* CPUs which require a guarantee of coherency (no inequivalent

2
arch/powerpc/include/asm/processor.h
View file

@ -400,6 +400,8 @@ static inline unsigned long __pack_fe01(unsigned int fpmode)
#define cpu_relax() barrier()
#endif
#define cpu_relax_lowlatency() cpu_relax()
/* Check that a certain kernel stack pointer is valid in task_struct p */
int validate_sp(unsigned long sp, struct task_struct *p,
unsigned long nbytes);

2
arch/s390/include/asm/processor.h
View file

@ -217,7 +217,7 @@ static inline void cpu_relax(void)
barrier();
}
#define arch_mutex_cpu_relax() barrier()
#define cpu_relax_lowlatency() barrier()
static inline void psw_set_key(unsigned int key)
{

1
arch/score/include/asm/processor.h
View file

@ -24,6 +24,7 @@ extern unsigned long get_wchan(struct task_struct *p);
#define current_text_addr() ({ __label__ _l; _l: &&_l; })
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
#define release_thread(thread) do {} while (0)
/*

1
arch/sh/include/asm/processor.h
View file

@ -97,6 +97,7 @@ extern struct sh_cpuinfo cpu_data[];
#define cpu_sleep() __asm__ __volatile__ ("sleep" : : : "memory")
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
void default_idle(void);
void stop_this_cpu(void *);

2
arch/sparc/include/asm/processor_32.h
View file

@ -119,6 +119,8 @@ extern struct task_struct *last_task_used_math;
int do_mathemu(struct pt_regs *regs, struct task_struct *fpt);
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
extern void (*sparc_idle)(void);
#endif

1
arch/sparc/include/asm/processor_64.h
View file

@ -216,6 +216,7 @@ unsigned long get_wchan(struct task_struct *task);
"nop\n\t" \
".previous" \
::: "memory")
#define cpu_relax_lowlatency() cpu_relax()
/* Prefetch support. This is tuned for UltraSPARC-III and later.
* UltraSPARC-I will treat these as nops, and UltraSPARC-II has

2
arch/tile/include/asm/processor.h
View file

@ -266,6 +266,8 @@ static inline void cpu_relax(void)
barrier();
}
#define cpu_relax_lowlatency() cpu_relax()
/* Info on this processor (see fs/proc/cpuinfo.c) */
struct seq_operations;
extern const struct seq_operations cpuinfo_op;

1
arch/unicore32/include/asm/processor.h
View file

@ -71,6 +71,7 @@ extern void release_thread(struct task_struct *);
unsigned long get_wchan(struct task_struct *p);
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
#define task_pt_regs(p) \
((struct pt_regs *)(THREAD_START_SP + task_stack_page(p)) - 1)

2
arch/x86/include/asm/barrier.h
View file

@ -99,7 +99,7 @@
#if defined(CONFIG_X86_PPRO_FENCE)
/*
* For either of these options x86 doesn't have a strong TSO memory
* For this option x86 doesn't have a strong TSO memory
* model and we should fall back to full barriers.
*/

2
arch/x86/include/asm/processor.h
View file

@ -696,6 +696,8 @@ static inline void cpu_relax(void)
rep_nop();
}
#define cpu_relax_lowlatency() cpu_relax()
/* Stop speculative execution and prefetching of modified code. */
static inline void sync_core(void)
{

2
arch/x86/include/asm/qrwlock.h
View file

@ -3,7 +3,7 @@
#include <asm-generic/qrwlock_types.h>
#if !defined(CONFIG_X86_OOSTORE) && !defined(CONFIG_X86_PPRO_FENCE)
#ifndef CONFIG_X86_PPRO_FENCE
#define queue_write_unlock queue_write_unlock
static inline void queue_write_unlock(struct qrwlock *lock)
{

3
arch/x86/um/asm/processor.h
View file

@ -25,7 +25,8 @@ static inline void rep_nop(void)
__asm__ __volatile__("rep;nop": : :"memory");
}
#define cpu_relax() rep_nop()
#define cpu_relax() rep_nop()
#define cpu_relax_lowlatency() cpu_relax()
#include <asm/processor-generic.h>

1
arch/xtensa/include/asm/processor.h
View file

@ -182,6 +182,7 @@ extern unsigned long get_wchan(struct task_struct *p);
#define KSTK_ESP(tsk) (task_pt_regs(tsk)->areg[1])
#define cpu_relax() barrier()
#define cpu_relax_lowlatency() cpu_relax()
/* Special register access. */

4
include/linux/mutex.h
View file

@ -176,8 +176,4 @@ extern void mutex_unlock(struct mutex *lock);
extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
#ifndef arch_mutex_cpu_relax
# define arch_mutex_cpu_relax() cpu_relax()
#endif
#endif /* __LINUX_MUTEX_H */

6
include/linux/rtmutex.h
View file

@ -90,11 +90,9 @@ extern void __rt_mutex_init(struct rt_mutex *lock, const char *name);
extern void rt_mutex_destroy(struct rt_mutex *lock);
extern void rt_mutex_lock(struct rt_mutex *lock);
extern int rt_mutex_lock_interruptible(struct rt_mutex *lock,
int detect_deadlock);
extern int rt_mutex_lock_interruptible(struct rt_mutex *lock);
extern int rt_mutex_timed_lock(struct rt_mutex *lock,
struct hrtimer_sleeper *timeout,
int detect_deadlock);
struct hrtimer_sleeper *timeout);
extern int rt_mutex_trylock(struct rt_mutex *lock);

2
include/linux/seqlock.h
View file

@ -164,8 +164,6 @@ static inline unsigned read_seqcount_begin(const seqcount_t *s)
static inline unsigned raw_seqcount_begin(const seqcount_t *s)
{
unsigned ret = ACCESS_ONCE(s->sequence);
seqcount_lockdep_reader_access(s);
smp_rmb();
return ret & ~1;
}

410
kernel/futex.c
View file

@ -792,93 +792,90 @@ void exit_pi_state_list(struct task_struct *curr)
* [10] There is no transient state which leaves owner and user space
* TID out of sync.
*/
static int
lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
union futex_key *key, struct futex_pi_state **ps)
/*
* Validate that the existing waiter has a pi_state and sanity check
* the pi_state against the user space value. If correct, attach to
* it.
*/
static int attach_to_pi_state(u32 uval, struct futex_pi_state *pi_state,
struct futex_pi_state **ps)
{
struct futex_pi_state *pi_state = NULL;
struct futex_q *this, *next;
struct task_struct *p;
pid_t pid = uval & FUTEX_TID_MASK;
plist_for_each_entry_safe(this, next, &hb->chain, list) {
if (match_futex(&this->key, key)) {
/*
* Userspace might have messed up non-PI and PI futexes [3]
*/
if (unlikely(!pi_state))
return -EINVAL;
WARN_ON(!atomic_read(&pi_state->refcount));
/*
* Handle the owner died case:
*/
if (uval & FUTEX_OWNER_DIED) {
/*
* exit_pi_state_list sets owner to NULL and wakes the
* topmost waiter. The task which acquires the
* pi_state->rt_mutex will fixup owner.
*/
if (!pi_state->owner) {
/*
* Sanity check the waiter before increasing
* the refcount and attaching to it.
* No pi state owner, but the user space TID
* is not 0. Inconsistent state. [5]
*/
pi_state = this->pi_state;
/*
* Userspace might have messed up non-PI and
* PI futexes [3]
*/
if (unlikely(!pi_state))
if (pid)
return -EINVAL;
WARN_ON(!atomic_read(&pi_state->refcount));
/*
* Handle the owner died case:
* Take a ref on the state and return success. [4]
*/
if (uval & FUTEX_OWNER_DIED) {
/*
* exit_pi_state_list sets owner to NULL and
* wakes the topmost waiter. The task which
* acquires the pi_state->rt_mutex will fixup
* owner.
*/
if (!pi_state->owner) {
/*
* No pi state owner, but the user
* space TID is not 0. Inconsistent
* state. [5]
*/
if (pid)
return -EINVAL;
/*
* Take a ref on the state and
* return. [4]
*/
goto out_state;
}
/*
* If TID is 0, then either the dying owner
* has not yet executed exit_pi_state_list()
* or some waiter acquired the rtmutex in the
* pi state, but did not yet fixup the TID in
* user space.
*
* Take a ref on the state and return. [6]
*/
if (!pid)
goto out_state;
} else {
/*
* If the owner died bit is not set,
* then the pi_state must have an
* owner. [7]
*/
if (!pi_state->owner)
return -EINVAL;
}
/*
* Bail out if user space manipulated the
* futex value. If pi state exists then the
* owner TID must be the same as the user
* space TID. [9/10]
*/
if (pid != task_pid_vnr(pi_state->owner))
return -EINVAL;
out_state:
atomic_inc(&pi_state->refcount);
*ps = pi_state;
return 0;
goto out_state;
}
/*
* If TID is 0, then either the dying owner has not
* yet executed exit_pi_state_list() or some waiter
* acquired the rtmutex in the pi state, but did not
* yet fixup the TID in user space.
*
* Take a ref on the state and return success. [6]
*/
if (!pid)
goto out_state;
} else {
/*
* If the owner died bit is not set, then the pi_state
* must have an owner. [7]
*/
if (!pi_state->owner)
return -EINVAL;
}
/*
* Bail out if user space manipulated the futex value. If pi
* state exists then the owner TID must be the same as the
* user space TID. [9/10]
*/
if (pid != task_pid_vnr(pi_state->owner))
return -EINVAL;
out_state:
atomic_inc(&pi_state->refcount);
*ps = pi_state;
return 0;
}
/*
* Lookup the task for the TID provided from user space and attach to
* it after doing proper sanity checks.
*/
static int attach_to_pi_owner(u32 uval, union futex_key *key,
struct futex_pi_state **ps)
{
pid_t pid = uval & FUTEX_TID_MASK;
struct futex_pi_state *pi_state;
struct task_struct *p;
/*
* We are the first waiter - try to look up the real owner and attach
* the new pi_state to it, but bail out when TID = 0 [1]
@ -920,7 +917,7 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
pi_state = alloc_pi_state();
/*
* Initialize the pi_mutex in locked state and make 'p'
* Initialize the pi_mutex in locked state and make @p
* the owner of it:
*/
rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
@ -940,6 +937,36 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
return 0;
}
static int lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
union futex_key *key, struct futex_pi_state **ps)
{
struct futex_q *match = futex_top_waiter(hb, key);
/*
* If there is a waiter on that futex, validate it and
* attach to the pi_state when the validation succeeds.
*/
if (match)
return attach_to_pi_state(uval, match->pi_state, ps);
/*
* We are the first waiter - try to look up the owner based on
* @uval and attach to it.
*/
return attach_to_pi_owner(uval, key, ps);
}
static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
{
u32 uninitialized_var(curval);
if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
return -EFAULT;
/*If user space value changed, let the caller retry */
return curval != uval ? -EAGAIN : 0;
}
/**
* futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
* @uaddr: the pi futex user address
@ -963,113 +990,69 @@ static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
struct futex_pi_state **ps,
struct task_struct *task, int set_waiters)
{
int lock_taken, ret, force_take = 0;
u32 uval, newval, curval, vpid = task_pid_vnr(task);
retry:
ret = lock_taken = 0;
u32 uval, newval, vpid = task_pid_vnr(task);
struct futex_q *match;
int ret;
/*
* To avoid races, we attempt to take the lock here again
* (by doing a 0 -> TID atomic cmpxchg), while holding all
* the locks. It will most likely not succeed.
* Read the user space value first so we can validate a few
* things before proceeding further.
*/
newval = vpid;
if (set_waiters)
newval |= FUTEX_WAITERS;
if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, 0, newval)))
if (get_futex_value_locked(&uval, uaddr))
return -EFAULT;
/*
* Detect deadlocks.
*/
if ((unlikely((curval & FUTEX_TID_MASK) == vpid)))
if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
return -EDEADLK;
/*
* Surprise - we got the lock, but we do not trust user space at all.
* Lookup existing state first. If it exists, try to attach to
* its pi_state.
*/
if (unlikely(!curval)) {
match = futex_top_waiter(hb, key);
if (match)
return attach_to_pi_state(uval, match->pi_state, ps);
/*
* No waiter and user TID is 0. We are here because the
* waiters or the owner died bit is set or called from
* requeue_cmp_pi or for whatever reason something took the
* syscall.
*/
if (!(uval & FUTEX_TID_MASK)) {
/*
* We verify whether there is kernel state for this
* futex. If not, we can safely assume, that the 0 ->
* TID transition is correct. If state exists, we do
* not bother to fixup the user space state as it was
* corrupted already.
* We take over the futex. No other waiters and the user space
* TID is 0. We preserve the owner died bit.
*/
return futex_top_waiter(hb, key) ? -EINVAL : 1;
newval = uval & FUTEX_OWNER_DIED;
newval |= vpid;
/* The futex requeue_pi code can enforce the waiters bit */
if (set_waiters)
newval |= FUTEX_WAITERS;
ret = lock_pi_update_atomic(uaddr, uval, newval);
/* If the take over worked, return 1 */
return ret < 0 ? ret : 1;
}
uval = curval;
/*
* Set the FUTEX_WAITERS flag, so the owner will know it has someone
* to wake at the next unlock.
* First waiter. Set the waiters bit before attaching ourself to
* the owner. If owner tries to unlock, it will be forced into
* the kernel and blocked on hb->lock.
*/
newval = curval | FUTEX_WAITERS;
newval = uval | FUTEX_WAITERS;
ret = lock_pi_update_atomic(uaddr, uval, newval);
if (ret)
return ret;
/*
* Should we force take the futex? See below.
* If the update of the user space value succeeded, we try to
* attach to the owner. If that fails, no harm done, we only
* set the FUTEX_WAITERS bit in the user space variable.
*/
if (unlikely(force_take)) {
/*
* Keep the OWNER_DIED and the WAITERS bit and set the
* new TID value.
*/
newval = (curval & ~FUTEX_TID_MASK) | vpid;
force_take = 0;
lock_taken = 1;
}
if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
return -EFAULT;
if (unlikely(curval != uval))
goto retry;
/*
* We took the lock due to forced take over.
*/
if (unlikely(lock_taken))
return 1;
/*
* We dont have the lock. Look up the PI state (or create it if
* we are the first waiter):
*/
ret = lookup_pi_state(uval, hb, key, ps);
if (unlikely(ret)) {
switch (ret) {
case -ESRCH:
/*
* We failed to find an owner for this
* futex. So we have no pi_state to block
* on. This can happen in two cases:
*
* 1) The owner died
* 2) A stale FUTEX_WAITERS bit
*
* Re-read the futex value.
*/
if (get_futex_value_locked(&curval, uaddr))
return -EFAULT;
/*
* If the owner died or we have a stale
* WAITERS bit the owner TID in the user space
* futex is 0.
*/
if (!(curval & FUTEX_TID_MASK)) {
force_take = 1;
goto retry;
}
default:
break;
}
}
return ret;
return attach_to_pi_owner(uval, key, ps);
}
/**
@ -1186,22 +1169,6 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
return 0;
}
static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
{
u32 uninitialized_var(oldval);
/*
* There is no waiter, so we unlock the futex. The owner died
* bit has not to be preserved here. We are the owner:
*/
if (cmpxchg_futex_value_locked(&oldval, uaddr, uval, 0))
return -EFAULT;
if (oldval != uval)
return -EAGAIN;
return 0;
}
/*
* Express the locking dependencies for lockdep:
*/
@ -1659,7 +1626,12 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
goto retry;
goto out;
case -EAGAIN:
/* The owner was exiting, try again. */
/*
* Two reasons for this:
* - Owner is exiting and we just wait for the
* exit to complete.
* - The user space value changed.
*/
double_unlock_hb(hb1, hb2);
hb_waiters_dec(hb2);
put_futex_key(&key2);
@ -1718,7 +1690,7 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
this->pi_state = pi_state;
ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
this->rt_waiter,
this->task, 1);
this->task);
if (ret == 1) {
/* We got the lock. */
requeue_pi_wake_futex(this, &key2, hb2);
@ -2316,8 +2288,10 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
goto uaddr_faulted;
case -EAGAIN:
/*
* Task is exiting and we just wait for the
* exit to complete.
* Two reasons for this:
* - Task is exiting and we just wait for the
* exit to complete.
* - The user space value changed.
*/
queue_unlock(hb);
put_futex_key(&q.key);
@ -2337,9 +2311,9 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
/*
* Block on the PI mutex:
*/
if (!trylock)
ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
else {
if (!trylock) {
ret = rt_mutex_timed_futex_lock(&q.pi_state->pi_mutex, to);
} else {
ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
/* Fixup the trylock return value: */
ret = ret ? 0 : -EWOULDBLOCK;
@ -2401,10 +2375,10 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
*/
static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
{
struct futex_hash_bucket *hb;
struct futex_q *this, *next;
u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
union futex_key key = FUTEX_KEY_INIT;
u32 uval, vpid = task_pid_vnr(current);
struct futex_hash_bucket *hb;
struct futex_q *match;
int ret;
retry:
@ -2417,57 +2391,47 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
return -EPERM;
ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
if (unlikely(ret != 0))
goto out;
if (ret)
return ret;
hb = hash_futex(&key);
spin_lock(&hb->lock);
/*
* To avoid races, try to do the TID -> 0 atomic transition
* again. If it succeeds then we can return without waking
* anyone else up. We only try this if neither the waiters nor
* the owner died bit are set.
* Check waiters first. We do not trust user space values at
* all and we at least want to know if user space fiddled
* with the futex value instead of blindly unlocking.
*/
if (!(uval & ~FUTEX_TID_MASK) &&
cmpxchg_futex_value_locked(&uval, uaddr, vpid, 0))
goto pi_faulted;
/*
* Rare case: we managed to release the lock atomically,
* no need to wake anyone else up:
*/
if (unlikely(uval == vpid))
goto out_unlock;
/*
* Ok, other tasks may need to be woken up - check waiters
* and do the wakeup if necessary:
*/
plist_for_each_entry_safe(this, next, &hb->chain, list) {
if (!match_futex (&this->key, &key))
continue;
ret = wake_futex_pi(uaddr, uval, this);
match = futex_top_waiter(hb, &key);
if (match) {
ret = wake_futex_pi(uaddr, uval, match);
/*
* The atomic access to the futex value
* generated a pagefault, so retry the
* user-access and the wakeup:
* The atomic access to the futex value generated a
* pagefault, so retry the user-access and the wakeup:
*/
if (ret == -EFAULT)
goto pi_faulted;
goto out_unlock;
}
/*
* No waiters - kernel unlocks the futex:
* We have no kernel internal state, i.e. no waiters in the
* kernel. Waiters which are about to queue themselves are stuck
* on hb->lock. So we can safely ignore them. We do neither
* preserve the WAITERS bit not the OWNER_DIED one. We are the
* owner.
*/
ret = unlock_futex_pi(uaddr, uval);
if (ret == -EFAULT)
if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))
goto pi_faulted;
/*
* If uval has changed, let user space handle it.
*/
ret = (curval == uval) ? 0 : -EAGAIN;
out_unlock:
spin_unlock(&hb->lock);
put_futex_key(&key);
out:
return ret;
pi_faulted:
@ -2669,7 +2633,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
*/
WARN_ON(!q.pi_state);
pi_mutex = &q.pi_state->pi_mutex;
ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter);
debug_rt_mutex_free_waiter(&rt_waiter);
spin_lock(q.lock_ptr);

2
kernel/locking/lockdep.c
View file

@ -384,7 +384,9 @@ static void print_lockdep_off(const char *bug_msg)
{
printk(KERN_DEBUG "%s\n", bug_msg);
printk(KERN_DEBUG "turning off the locking correctness validator.\n");
#ifdef CONFIG_LOCK_STAT
printk(KERN_DEBUG "Please attach the output of /proc/lock_stat to the bug report\n");
#endif
}
static int save_trace(struct stack_trace *trace)

8
kernel/locking/mcs_spinlock.c
View file

@ -1,6 +1,4 @@
#include <linux/percpu.h>
#include <linux/mutex.h>
#include <linux/sched.h>
#include "mcs_spinlock.h"
@ -79,7 +77,7 @@ osq_wait_next(struct optimistic_spin_queue *lock,
break;
}
arch_mutex_cpu_relax();
cpu_relax_lowlatency();
}
return next;
@ -120,7 +118,7 @@ bool osq_lock(struct optimistic_spin_queue *lock)
if (need_resched())
goto unqueue;
arch_mutex_cpu_relax();
cpu_relax_lowlatency();
}
return true;
@ -146,7 +144,7 @@ bool osq_lock(struct optimistic_spin_queue *lock)
if (smp_load_acquire(&node->locked))
return true;
arch_mutex_cpu_relax();
cpu_relax_lowlatency();
/*
* Or we race against a concurrent unqueue()'s step-B, in which

4
kernel/locking/mcs_spinlock.h
View file

@ -27,7 +27,7 @@ struct mcs_spinlock {
#define arch_mcs_spin_lock_contended(l) \
do { \
while (!(smp_load_acquire(l))) \
arch_mutex_cpu_relax(); \
cpu_relax_lowlatency(); \
} while (0)
#endif
@ -104,7 +104,7 @@ void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
return;
/* Wait until the next pointer is set */
while (!(next = ACCESS_ONCE(node->next)))
arch_mutex_cpu_relax();
cpu_relax_lowlatency();
}
/* Pass lock to next waiter. */

39
kernel/locking/mutex.c
View file

@ -46,12 +46,6 @@
# include <asm/mutex.h>
#endif
/*
* A negative mutex count indicates that waiters are sleeping waiting for the
* mutex.
*/
#define MUTEX_SHOW_NO_WAITER(mutex) (atomic_read(&(mutex)->count) >= 0)
void
__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
{
@ -152,7 +146,7 @@ int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
if (need_resched())
break;
arch_mutex_cpu_relax();
cpu_relax_lowlatency();
}
rcu_read_unlock();
@ -388,12 +382,10 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
/*
* Optimistic spinning.
*
* We try to spin for acquisition when we find that there are no
* pending waiters and the lock owner is currently running on a
* (different) CPU.
*
* The rationale is that if the lock owner is running, it is likely to
* release the lock soon.
* We try to spin for acquisition when we find that the lock owner
* is currently running on a (different) CPU and while we don't
* need to reschedule. The rationale is that if the lock owner is
* running, it is likely to release the lock soon.
*
* Since this needs the lock owner, and this mutex implementation
* doesn't track the owner atomically in the lock field, we need to
@ -440,7 +432,8 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
if (owner && !mutex_spin_on_owner(lock, owner))
break;
if ((atomic_read(&lock->count) == 1) &&
/* Try to acquire the mutex if it is unlocked. */
if (!mutex_is_locked(lock) &&
(atomic_cmpxchg(&lock->count, 1, 0) == 1)) {
lock_acquired(&lock->dep_map, ip);
if (use_ww_ctx) {
@ -471,7 +464,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
* memory barriers as we'll eventually observe the right
* values at the cost of a few extra spins.
*/
arch_mutex_cpu_relax();
cpu_relax_lowlatency();
}
osq_unlock(&lock->osq);
slowpath:
@ -485,8 +478,11 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
#endif
spin_lock_mutex(&lock->wait_lock, flags);
/* once more, can we acquire the lock? */
if (MUTEX_SHOW_NO_WAITER(lock) && (atomic_xchg(&lock->count, 0) == 1))
/*
* Once more, try to acquire the lock. Only try-lock the mutex if
* it is unlocked to reduce unnecessary xchg() operations.
*/
if (!mutex_is_locked(lock) && (atomic_xchg(&lock->count, 0) == 1))
goto skip_wait;
debug_mutex_lock_common(lock, &waiter);
@ -506,9 +502,10 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
* it's unlocked. Later on, if we sleep, this is the
* operation that gives us the lock. We xchg it to -1, so
* that when we release the lock, we properly wake up the
* other waiters:
* other waiters. We only attempt the xchg if the count is
* non-negative in order to avoid unnecessary xchg operations:
*/
if (MUTEX_SHOW_NO_WAITER(lock) &&
if (atomic_read(&lock->count) >= 0 &&
(atomic_xchg(&lock->count, -1) == 1))
break;
@ -823,6 +820,10 @@ static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
unsigned long flags;
int prev;
/* No need to trylock if the mutex is locked. */
if (mutex_is_locked(lock))
return 0;
spin_lock_mutex(&lock->wait_lock, flags);
prev = atomic_xchg(&lock->count, -1);

9
kernel/locking/qrwlock.c
View file

@ -20,7 +20,6 @@
#include <linux/cpumask.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/mutex.h>
#include <asm/qrwlock.h>
/**
@ -35,7 +34,7 @@ static __always_inline void
rspin_until_writer_unlock(struct qrwlock *lock, u32 cnts)
{
while ((cnts & _QW_WMASK) == _QW_LOCKED) {
arch_mutex_cpu_relax();
cpu_relax_lowlatency();
cnts = smp_load_acquire((u32 *)&lock->cnts);
}
}
@ -75,7 +74,7 @@ void queue_read_lock_slowpath(struct qrwlock *lock)
* to make sure that the write lock isn't taken.
*/
while (atomic_read(&lock->cnts) & _QW_WMASK)
arch_mutex_cpu_relax();
cpu_relax_lowlatency();
cnts = atomic_add_return(_QR_BIAS, &lock->cnts) - _QR_BIAS;
rspin_until_writer_unlock(lock, cnts);
@ -114,7 +113,7 @@ void queue_write_lock_slowpath(struct qrwlock *lock)
cnts | _QW_WAITING) == cnts))
break;
arch_mutex_cpu_relax();
cpu_relax_lowlatency();
}
/* When no more readers, set the locked flag */
@ -125,7 +124,7 @@ void queue_write_lock_slowpath(struct qrwlock *lock)
_QW_LOCKED) == _QW_WAITING))
break;
arch_mutex_cpu_relax();
cpu_relax_lowlatency();
}
unlock:
arch_spin_unlock(&lock->lock);

5
kernel/locking/rtmutex-debug.c
View file

@ -66,12 +66,13 @@ void rt_mutex_debug_task_free(struct task_struct *task)
* the deadlock. We print when we return. act_waiter can be NULL in
* case of a remove waiter operation.
*/
void debug_rt_mutex_deadlock(int detect, struct rt_mutex_waiter *act_waiter,
void debug_rt_mutex_deadlock(enum rtmutex_chainwalk chwalk,
struct rt_mutex_waiter *act_waiter,
struct rt_mutex *lock)
{
struct task_struct *task;
if (!debug_locks || detect || !act_waiter)
if (!debug_locks || chwalk == RT_MUTEX_FULL_CHAINWALK || !act_waiter)
return;
task = rt_mutex_owner(act_waiter->lock);

7
kernel/locking/rtmutex-debug.h
View file

@ -20,14 +20,15 @@ extern void debug_rt_mutex_unlock(struct rt_mutex *lock);
extern void debug_rt_mutex_proxy_lock(struct rt_mutex *lock,
struct task_struct *powner);
extern void debug_rt_mutex_proxy_unlock(struct rt_mutex *lock);
extern void debug_rt_mutex_deadlock(int detect, struct rt_mutex_waiter *waiter,
extern void debug_rt_mutex_deadlock(enum rtmutex_chainwalk chwalk,
struct rt_mutex_waiter *waiter,
struct rt_mutex *lock);
extern void debug_rt_mutex_print_deadlock(struct rt_mutex_waiter *waiter);
# define debug_rt_mutex_reset_waiter(w) \
do { (w)->deadlock_lock = NULL; } while (0)
static inline int debug_rt_mutex_detect_deadlock(struct rt_mutex_waiter *waiter,
int detect)
static inline bool debug_rt_mutex_detect_deadlock(struct rt_mutex_waiter *waiter,
enum rtmutex_chainwalk walk)
{
return (waiter != NULL);
}

576
kernel/locking/rtmutex.c
View file

@ -307,6 +307,32 @@ static void rt_mutex_adjust_prio(struct task_struct *task)
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
}
/*
* Deadlock detection is conditional:
*
* If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
* if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
*
* If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
* conducted independent of the detect argument.
*
* If the waiter argument is NULL this indicates the deboost path and
* deadlock detection is disabled independent of the detect argument
* and the config settings.
*/
static bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
enum rtmutex_chainwalk chwalk)
{
/*
* This is just a wrapper function for the following call,
* because debug_rt_mutex_detect_deadlock() smells like a magic
* debug feature and I wanted to keep the cond function in the
* main source file along with the comments instead of having
* two of the same in the headers.
*/
return debug_rt_mutex_detect_deadlock(waiter, chwalk);
}
/*
* Max number of times we'll walk the boosting chain:
*/
@ -337,21 +363,65 @@ static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
* @top_task: the current top waiter
*
* Returns 0 or -EDEADLK.
*
* Chain walk basics and protection scope
*
* [R] refcount on task
* [P] task->pi_lock held
* [L] rtmutex->wait_lock held
*
* Step Description Protected by
* function arguments:
* @task [R]
* @orig_lock if != NULL @top_task is blocked on it
* @next_lock Unprotected. Cannot be
* dereferenced. Only used for
* comparison.
* @orig_waiter if != NULL @top_task is blocked on it
* @top_task current, or in case of proxy
* locking protected by calling
* code
* again:
* loop_sanity_check();
* retry:
* [1] lock(task->pi_lock); [R] acquire [P]
* [2] waiter = task->pi_blocked_on; [P]
* [3] check_exit_conditions_1(); [P]
* [4] lock = waiter->lock; [P]
* [5] if (!try_lock(lock->wait_lock)) { [P] try to acquire [L]
* unlock(task->pi_lock); release [P]
* goto retry;
* }
* [6] check_exit_conditions_2(); [P] + [L]
* [7] requeue_lock_waiter(lock, waiter); [P] + [L]
* [8] unlock(task->pi_lock); release [P]
* put_task_struct(task); release [R]
* [9] check_exit_conditions_3(); [L]
* [10] task = owner(lock); [L]
* get_task_struct(task); [L] acquire [R]
* lock(task->pi_lock); [L] acquire [P]
* [11] requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
* [12] check_exit_conditions_4(); [P] + [L]
* [13] unlock(task->pi_lock); release [P]
* unlock(lock->wait_lock); release [L]
* goto again;
*/
static int rt_mutex_adjust_prio_chain(struct task_struct *task,
int deadlock_detect,
enum rtmutex_chainwalk chwalk,
struct rt_mutex *orig_lock,
struct rt_mutex *next_lock,
struct rt_mutex_waiter *orig_waiter,
struct task_struct *top_task)
{
struct rt_mutex *lock;
struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
int detect_deadlock, ret = 0, depth = 0;
struct rt_mutex_waiter *prerequeue_top_waiter;
int ret = 0, depth = 0;
struct rt_mutex *lock;
bool detect_deadlock;
unsigned long flags;
bool requeue = true;
detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
deadlock_detect);
detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
/*
* The (de)boosting is a step by step approach with a lot of
@ -360,6 +430,9 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
* carefully whether things change under us.
*/
again:
/*
* We limit the lock chain length for each invocation.
*/
if (++depth > max_lock_depth) {
static int prev_max;
@ -377,13 +450,28 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
return -EDEADLK;
}
/*
* We are fully preemptible here and only hold the refcount on
* @task. So everything can have changed under us since the
* caller or our own code below (goto retry/again) dropped all
* locks.
*/
retry:
/*
* Task can not go away as we did a get_task() before !
* [1] Task cannot go away as we did a get_task() before !
*/
raw_spin_lock_irqsave(&task->pi_lock, flags);
/*
* [2] Get the waiter on which @task is blocked on.
*/
waiter = task->pi_blocked_on;
/*
* [3] check_exit_conditions_1() protected by task->pi_lock.
*/
/*
* Check whether the end of the boosting chain has been
* reached or the state of the chain has changed while we
@ -421,20 +509,41 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
goto out_unlock_pi;
/*
* If deadlock detection is off, we stop here if we
* are not the top pi waiter of the task.
* are not the top pi waiter of the task. If deadlock
* detection is enabled we continue, but stop the
* requeueing in the chain walk.
*/
if (!detect_deadlock && top_waiter != task_top_pi_waiter(task))
goto out_unlock_pi;
if (top_waiter != task_top_pi_waiter(task)) {
if (!detect_deadlock)
goto out_unlock_pi;
else
requeue = false;
}
}
/*
* When deadlock detection is off then we check, if further
* priority adjustment is necessary.
* If the waiter priority is the same as the task priority
* then there is no further priority adjustment necessary. If
* deadlock detection is off, we stop the chain walk. If its
* enabled we continue, but stop the requeueing in the chain
* walk.
*/
if (!detect_deadlock && waiter->prio == task->prio)
goto out_unlock_pi;
if (waiter->prio == task->prio) {
if (!detect_deadlock)
goto out_unlock_pi;
else
requeue = false;
}
/*
* [4] Get the next lock
*/
lock = waiter->lock;
/*
* [5] We need to trylock here as we are holding task->pi_lock,
* which is the reverse lock order versus the other rtmutex
* operations.
*/
if (!raw_spin_trylock(&lock->wait_lock)) {
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
cpu_relax();
@ -442,79 +551,180 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
}
/*
* [6] check_exit_conditions_2() protected by task->pi_lock and
* lock->wait_lock.
*
* Deadlock detection. If the lock is the same as the original
* lock which caused us to walk the lock chain or if the
* current lock is owned by the task which initiated the chain
* walk, we detected a deadlock.
*/
if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);
raw_spin_unlock(&lock->wait_lock);
ret = -EDEADLK;
goto out_unlock_pi;
}
top_waiter = rt_mutex_top_waiter(lock);
/*
* If we just follow the lock chain for deadlock detection, no
* need to do all the requeue operations. To avoid a truckload
* of conditionals around the various places below, just do the
* minimum chain walk checks.
*/
if (!requeue) {
/*
* No requeue[7] here. Just release @task [8]
*/
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
put_task_struct(task);
/* Requeue the waiter */
/*
* [9] check_exit_conditions_3 protected by lock->wait_lock.
* If there is no owner of the lock, end of chain.
*/
if (!rt_mutex_owner(lock)) {
raw_spin_unlock(&lock->wait_lock);
return 0;
}
/* [10] Grab the next task, i.e. owner of @lock */
task = rt_mutex_owner(lock);
get_task_struct(task);
raw_spin_lock_irqsave(&task->pi_lock, flags);
/*
* No requeue [11] here. We just do deadlock detection.
*
* [12] Store whether owner is blocked
* itself. Decision is made after dropping the locks
*/
next_lock = task_blocked_on_lock(task);
/*
* Get the top waiter for the next iteration
*/
top_waiter = rt_mutex_top_waiter(lock);
/* [13] Drop locks */
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
raw_spin_unlock(&lock->wait_lock);
/* If owner is not blocked, end of chain. */
if (!next_lock)
goto out_put_task;
goto again;
}
/*
* Store the current top waiter before doing the requeue
* operation on @lock. We need it for the boost/deboost
* decision below.
*/
prerequeue_top_waiter = rt_mutex_top_waiter(lock);
/* [7] Requeue the waiter in the lock waiter list. */
rt_mutex_dequeue(lock, waiter);
waiter->prio = task->prio;
rt_mutex_enqueue(lock, waiter);
/* Release the task */
/* [8] Release the task */
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
if (!rt_mutex_owner(lock)) {
/*
* If the requeue above changed the top waiter, then we need
* to wake the new top waiter up to try to get the lock.
*/
if (top_waiter != rt_mutex_top_waiter(lock))
wake_up_process(rt_mutex_top_waiter(lock)->task);
raw_spin_unlock(&lock->wait_lock);
goto out_put_task;
}
put_task_struct(task);
/* Grab the next task */
/*
* [9] check_exit_conditions_3 protected by lock->wait_lock.
*
* We must abort the chain walk if there is no lock owner even
* in the dead lock detection case, as we have nothing to
* follow here. This is the end of the chain we are walking.
*/
if (!rt_mutex_owner(lock)) {
/*
* If the requeue [7] above changed the top waiter,
* then we need to wake the new top waiter up to try
* to get the lock.
*/
if (prerequeue_top_waiter != rt_mutex_top_waiter(lock))
wake_up_process(rt_mutex_top_waiter(lock)->task);
raw_spin_unlock(&lock->wait_lock);
return 0;
}
/* [10] Grab the next task, i.e. the owner of @lock */
task = rt_mutex_owner(lock);
get_task_struct(task);
raw_spin_lock_irqsave(&task->pi_lock, flags);
/* [11] requeue the pi waiters if necessary */
if (waiter == rt_mutex_top_waiter(lock)) {
/* Boost the owner */
rt_mutex_dequeue_pi(task, top_waiter);
/*
* The waiter became the new top (highest priority)
* waiter on the lock. Replace the previous top waiter
* in the owner tasks pi waiters list with this waiter
* and adjust the priority of the owner.
*/
rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
rt_mutex_enqueue_pi(task, waiter);
__rt_mutex_adjust_prio(task);
} else if (top_waiter == waiter) {
/* Deboost the owner */
} else if (prerequeue_top_waiter == waiter) {
/*
* The waiter was the top waiter on the lock, but is
* no longer the top prority waiter. Replace waiter in
* the owner tasks pi waiters list with the new top
* (highest priority) waiter and adjust the priority
* of the owner.
* The new top waiter is stored in @waiter so that
* @waiter == @top_waiter evaluates to true below and
* we continue to deboost the rest of the chain.
*/
rt_mutex_dequeue_pi(task, waiter);
waiter = rt_mutex_top_waiter(lock);
rt_mutex_enqueue_pi(task, waiter);
__rt_mutex_adjust_prio(task);
} else {
/*
* Nothing changed. No need to do any priority
* adjustment.
*/
}
/*
* [12] check_exit_conditions_4() protected by task->pi_lock
* and lock->wait_lock. The actual decisions are made after we
* dropped the locks.
*
* Check whether the task which owns the current lock is pi
* blocked itself. If yes we store a pointer to the lock for
* the lock chain change detection above. After we dropped
* task->pi_lock next_lock cannot be dereferenced anymore.
*/
next_lock = task_blocked_on_lock(task);
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
/*
* Store the top waiter of @lock for the end of chain walk
* decision below.
*/
top_waiter = rt_mutex_top_waiter(lock);
/* [13] Drop the locks */
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
raw_spin_unlock(&lock->wait_lock);
/*
* Make the actual exit decisions [12], based on the stored
* values.
*
* We reached the end of the lock chain. Stop right here. No
* point to go back just to figure that out.
*/
if (!next_lock)
goto out_put_task;
/*
* If the current waiter is not the top waiter on the lock,
* then we can stop the chain walk here if we are not in full
* deadlock detection mode.
*/
if (!detect_deadlock && waiter != top_waiter)
goto out_put_task;
@ -533,76 +743,119 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
*
* Must be called with lock->wait_lock held.
*
* @lock: the lock to be acquired.
* @task: the task which wants to acquire the lock
* @waiter: the waiter that is queued to the lock's wait list. (could be NULL)
* @lock: The lock to be acquired.
* @task: The task which wants to acquire the lock
* @waiter: The waiter that is queued to the lock's wait list if the
* callsite called task_blocked_on_lock(), otherwise NULL
*/
static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
struct rt_mutex_waiter *waiter)
struct rt_mutex_waiter *waiter)
{
unsigned long flags;
/*
* We have to be careful here if the atomic speedups are
* enabled, such that, when
* - no other waiter is on the lock
* - the lock has been released since we did the cmpxchg
* the lock can be released or taken while we are doing the
* checks and marking the lock with RT_MUTEX_HAS_WAITERS.
* Before testing whether we can acquire @lock, we set the
* RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
* other tasks which try to modify @lock into the slow path
* and they serialize on @lock->wait_lock.
*
* The atomic acquire/release aware variant of
* mark_rt_mutex_waiters uses a cmpxchg loop. After setting
* the WAITERS bit, the atomic release / acquire can not
* happen anymore and lock->wait_lock protects us from the
* non-atomic case.
* The RT_MUTEX_HAS_WAITERS bit can have a transitional state
* as explained at the top of this file if and only if:
*
* Note, that this might set lock->owner =
* RT_MUTEX_HAS_WAITERS in the case the lock is not contended
* any more. This is fixed up when we take the ownership.
* This is the transitional state explained at the top of this file.
* - There is a lock owner. The caller must fixup the
* transient state if it does a trylock or leaves the lock
* function due to a signal or timeout.
*
* - @task acquires the lock and there are no other
* waiters. This is undone in rt_mutex_set_owner(@task) at
* the end of this function.
*/
mark_rt_mutex_waiters(lock);
/*
* If @lock has an owner, give up.
*/
if (rt_mutex_owner(lock))
return 0;
/*
* It will get the lock because of one of these conditions:
* 1) there is no waiter
* 2) higher priority than waiters
* 3) it is top waiter
* If @waiter != NULL, @task has already enqueued the waiter
* into @lock waiter list. If @waiter == NULL then this is a
* trylock attempt.
*/
if (rt_mutex_has_waiters(lock)) {
if (task->prio >= rt_mutex_top_waiter(lock)->prio) {
if (!waiter || waiter != rt_mutex_top_waiter(lock))
return 0;
}
}
if (waiter || rt_mutex_has_waiters(lock)) {
unsigned long flags;
struct rt_mutex_waiter *top;
raw_spin_lock_irqsave(&task->pi_lock, flags);
/* remove the queued waiter. */
if (waiter) {
rt_mutex_dequeue(lock, waiter);
task->pi_blocked_on = NULL;
}
if (waiter) {
/*
* If waiter is not the highest priority waiter of
* @lock, give up.
*/
if (waiter != rt_mutex_top_waiter(lock))
return 0;
/*
* We have to enqueue the top waiter(if it exists) into
* task->pi_waiters list.
* We can acquire the lock. Remove the waiter from the
* lock waiters list.
*/
rt_mutex_dequeue(lock, waiter);
} else {
/*
* If the lock has waiters already we check whether @task is
* eligible to take over the lock.
*
* If there are no other waiters, @task can acquire
* the lock. @task->pi_blocked_on is NULL, so it does
* not need to be dequeued.
*/
if (rt_mutex_has_waiters(lock)) {
top = rt_mutex_top_waiter(lock);
rt_mutex_enqueue_pi(task, top);
/*
* If @task->prio is greater than or equal to
* the top waiter priority (kernel view),
* @task lost.
*/
if (task->prio >= rt_mutex_top_waiter(lock)->prio)
return 0;
/*
* The current top waiter stays enqueued. We
* don't have to change anything in the lock
* waiters order.
*/
} else {
/*
* No waiters. Take the lock without the
* pi_lock dance.@task->pi_blocked_on is NULL
* and we have no waiters to enqueue in @task
* pi waiters list.
*/
goto takeit;
}
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
}
/*
* Clear @task->pi_blocked_on. Requires protection by
* @task->pi_lock. Redundant operation for the @waiter == NULL
* case, but conditionals are more expensive than a redundant
* store.
*/
raw_spin_lock_irqsave(&task->pi_lock, flags);
task->pi_blocked_on = NULL;
/*
* Finish the lock acquisition. @task is the new owner. If
* other waiters exist we have to insert the highest priority
* waiter into @task->pi_waiters list.
*/
if (rt_mutex_has_waiters(lock))
rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
raw_spin_unlock_irqrestore(&task->pi_lock, flags);
takeit:
/* We got the lock. */
debug_rt_mutex_lock(lock);
/*
* This either preserves the RT_MUTEX_HAS_WAITERS bit if there
* are still waiters or clears it.
*/
rt_mutex_set_owner(lock, task);
rt_mutex_deadlock_account_lock(lock, task);
@ -620,7 +873,7 @@ static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter,
struct task_struct *task,
int detect_deadlock)
enum rtmutex_chainwalk chwalk)
{
struct task_struct *owner = rt_mutex_owner(lock);
struct rt_mutex_waiter *top_waiter = waiter;
@ -666,7 +919,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
__rt_mutex_adjust_prio(owner);
if (owner->pi_blocked_on)
chain_walk = 1;
} else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) {
} else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
chain_walk = 1;
}
@ -691,7 +944,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
raw_spin_unlock(&lock->wait_lock);
res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock,
res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
next_lock, waiter, task);
raw_spin_lock(&lock->wait_lock);
@ -753,9 +1006,9 @@ static void wakeup_next_waiter(struct rt_mutex *lock)
static void remove_waiter(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter)
{
int first = (waiter == rt_mutex_top_waiter(lock));
bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
struct task_struct *owner = rt_mutex_owner(lock);
struct rt_mutex *next_lock = NULL;
struct rt_mutex *next_lock;
unsigned long flags;
raw_spin_lock_irqsave(&current->pi_lock, flags);
@ -763,29 +1016,31 @@ static void remove_waiter(struct rt_mutex *lock,
current->pi_blocked_on = NULL;
raw_spin_unlock_irqrestore(&current->pi_lock, flags);
if (!owner)
/*
* Only update priority if the waiter was the highest priority
* waiter of the lock and there is an owner to update.
*/
if (!owner || !is_top_waiter)
return;
if (first) {
raw_spin_lock_irqsave(&owner->pi_lock, flags);
raw_spin_lock_irqsave(&owner->pi_lock, flags);
rt_mutex_dequeue_pi(owner, waiter);
rt_mutex_dequeue_pi(owner, waiter);
if (rt_mutex_has_waiters(lock))
rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
if (rt_mutex_has_waiters(lock)) {
struct rt_mutex_waiter *next;
__rt_mutex_adjust_prio(owner);
next = rt_mutex_top_waiter(lock);
rt_mutex_enqueue_pi(owner, next);
}
__rt_mutex_adjust_prio(owner);
/* Store the lock on which owner is blocked or NULL */
next_lock = task_blocked_on_lock(owner);
/* Store the lock on which owner is blocked or NULL */
next_lock = task_blocked_on_lock(owner);
raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
}
raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
/*
* Don't walk the chain, if the owner task is not blocked
* itself.
*/
if (!next_lock)
return;
@ -794,7 +1049,8 @@ static void remove_waiter(struct rt_mutex *lock,
raw_spin_unlock(&lock->wait_lock);
rt_mutex_adjust_prio_chain(owner, 0, lock, next_lock, NULL, current);
rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
next_lock, NULL, current);
raw_spin_lock(&lock->wait_lock);
}
@ -824,7 +1080,8 @@ void rt_mutex_adjust_pi(struct task_struct *task)
/* gets dropped in rt_mutex_adjust_prio_chain()! */
get_task_struct(task);
rt_mutex_adjust_prio_chain(task, 0, NULL, next_lock, NULL, task);
rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
next_lock, NULL, task);
}
/**
@ -902,7 +1159,7 @@ static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
static int __sched
rt_mutex_slowlock(struct rt_mutex *lock, int state,
struct hrtimer_sleeper *timeout,
int detect_deadlock)
enum rtmutex_chainwalk chwalk)
{
struct rt_mutex_waiter waiter;
int ret = 0;
@ -928,7 +1185,7 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
timeout->task = NULL;
}
ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);
ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
if (likely(!ret))
ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
@ -937,7 +1194,7 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
if (unlikely(ret)) {
remove_waiter(lock, &waiter);
rt_mutex_handle_deadlock(ret, detect_deadlock, &waiter);
rt_mutex_handle_deadlock(ret, chwalk, &waiter);
}
/*
@ -960,22 +1217,31 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
/*
* Slow path try-lock function:
*/
static inline int
rt_mutex_slowtrylock(struct rt_mutex *lock)
static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
{
int ret = 0;
int ret;
/*
* If the lock already has an owner we fail to get the lock.
* This can be done without taking the @lock->wait_lock as
* it is only being read, and this is a trylock anyway.
*/
if (rt_mutex_owner(lock))
return 0;
/*
* The mutex has currently no owner. Lock the wait lock and
* try to acquire the lock.
*/
raw_spin_lock(&lock->wait_lock);
if (likely(rt_mutex_owner(lock) != current)) {
ret = try_to_take_rt_mutex(lock, current, NULL);
ret = try_to_take_rt_mutex(lock, current, NULL);
/*
* try_to_take_rt_mutex() sets the lock waiters
* bit unconditionally. Clean this up.
*/
fixup_rt_mutex_waiters(lock);
}
/*
* try_to_take_rt_mutex() sets the lock waiters bit
* unconditionally. Clean this up.
*/
fixup_rt_mutex_waiters(lock);
raw_spin_unlock(&lock->wait_lock);
@ -1053,30 +1319,31 @@ rt_mutex_slowunlock(struct rt_mutex *lock)
*/
static inline int
rt_mutex_fastlock(struct rt_mutex *lock, int state,
int detect_deadlock,
int (*slowfn)(struct rt_mutex *lock, int state,
struct hrtimer_sleeper *timeout,
int detect_deadlock))
enum rtmutex_chainwalk chwalk))
{
if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
rt_mutex_deadlock_account_lock(lock, current);
return 0;
} else
return slowfn(lock, state, NULL, detect_deadlock);
return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
}
static inline int
rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
struct hrtimer_sleeper *timeout, int detect_deadlock,
struct hrtimer_sleeper *timeout,
enum rtmutex_chainwalk chwalk,
int (*slowfn)(struct rt_mutex *lock, int state,
struct hrtimer_sleeper *timeout,
int detect_deadlock))
enum rtmutex_chainwalk chwalk))
{
if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
likely(rt_mutex_cmpxchg(lock, NULL, current))) {
rt_mutex_deadlock_account_lock(lock, current);
return 0;
} else
return slowfn(lock, state, timeout, detect_deadlock);
return slowfn(lock, state, timeout, chwalk);
}
static inline int
@ -1109,54 +1376,61 @@ void __sched rt_mutex_lock(struct rt_mutex *lock)
{
might_sleep();
rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
}
EXPORT_SYMBOL_GPL(rt_mutex_lock);
/**
* rt_mutex_lock_interruptible - lock a rt_mutex interruptible
*
* @lock: the rt_mutex to be locked
* @detect_deadlock: deadlock detection on/off
* @lock: the rt_mutex to be locked
*
* Returns:
* 0 on success
* -EINTR when interrupted by a signal
* -EDEADLK when the lock would deadlock (when deadlock detection is on)
* 0 on success
* -EINTR when interrupted by a signal
*/
int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
int detect_deadlock)
int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
{
might_sleep();
return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
detect_deadlock, rt_mutex_slowlock);
return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
}
EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
/*
* Futex variant with full deadlock detection.
*/
int rt_mutex_timed_futex_lock(struct rt_mutex *lock,
struct hrtimer_sleeper *timeout)
{
might_sleep();
return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
RT_MUTEX_FULL_CHAINWALK,
rt_mutex_slowlock);
}
/**
* rt_mutex_timed_lock - lock a rt_mutex interruptible
* the timeout structure is provided
* by the caller
*
* @lock: the rt_mutex to be locked
* @lock: the rt_mutex to be locked
* @timeout: timeout structure or NULL (no timeout)
* @detect_deadlock: deadlock detection on/off
*
* Returns:
* 0 on success
* -EINTR when interrupted by a signal
* 0 on success
* -EINTR when interrupted by a signal
* -ETIMEDOUT when the timeout expired
* -EDEADLK when the lock would deadlock (when deadlock detection is on)
*/
int
rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
int detect_deadlock)
rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout)
{
might_sleep();
return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
detect_deadlock, rt_mutex_slowlock);
RT_MUTEX_MIN_CHAINWALK,
rt_mutex_slowlock);
}
EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
@ -1262,7 +1536,6 @@ void rt_mutex_proxy_unlock(struct rt_mutex *lock,
* @lock: the rt_mutex to take
* @waiter: the pre-initialized rt_mutex_waiter
* @task: the task to prepare
* @detect_deadlock: perform deadlock detection (1) or not (0)
*
* Returns:
* 0 - task blocked on lock
@ -1273,7 +1546,7 @@ void rt_mutex_proxy_unlock(struct rt_mutex *lock,
*/
int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter,
struct task_struct *task, int detect_deadlock)
struct task_struct *task)
{
int ret;
@ -1285,7 +1558,8 @@ int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
}
/* We enforce deadlock detection for futexes */
ret = task_blocks_on_rt_mutex(lock, waiter, task, 1);
ret = task_blocks_on_rt_mutex(lock, waiter, task,
RT_MUTEX_FULL_CHAINWALK);
if (ret && !rt_mutex_owner(lock)) {
/*
@ -1331,22 +1605,20 @@ struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
* rt_mutex_finish_proxy_lock() - Complete lock acquisition
* @lock: the rt_mutex we were woken on
* @to: the timeout, null if none. hrtimer should already have
* been started.
* been started.
* @waiter: the pre-initialized rt_mutex_waiter
* @detect_deadlock: perform deadlock detection (1) or not (0)
*
* Complete the lock acquisition started our behalf by another thread.
*
* Returns:
* 0 - success
* <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
* <0 - error, one of -EINTR, -ETIMEDOUT
*
* Special API call for PI-futex requeue support
*/
int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
struct hrtimer_sleeper *to,
struct rt_mutex_waiter *waiter,
int detect_deadlock)
struct rt_mutex_waiter *waiter)
{
int ret;

7
kernel/locking/rtmutex.h
View file

@ -22,10 +22,15 @@
#define debug_rt_mutex_init(m, n) do { } while (0)
#define debug_rt_mutex_deadlock(d, a ,l) do { } while (0)
#define debug_rt_mutex_print_deadlock(w) do { } while (0)
#define debug_rt_mutex_detect_deadlock(w,d) (d)
#define debug_rt_mutex_reset_waiter(w) do { } while (0)
static inline void rt_mutex_print_deadlock(struct rt_mutex_waiter *w)
{
WARN(1, "rtmutex deadlock detected\n");
}
static inline bool debug_rt_mutex_detect_deadlock(struct rt_mutex_waiter *w,
enum rtmutex_chainwalk walk)
{
return walk == RT_MUTEX_FULL_CHAINWALK;
}

22
kernel/locking/rtmutex_common.h
View file

@ -101,6 +101,21 @@ static inline struct task_struct *rt_mutex_owner(struct rt_mutex *lock)
((unsigned long)lock->owner & ~RT_MUTEX_OWNER_MASKALL);
}
/*
* Constants for rt mutex functions which have a selectable deadlock
* detection.
*
* RT_MUTEX_MIN_CHAINWALK: Stops the lock chain walk when there are
* no further PI adjustments to be made.
*
* RT_MUTEX_FULL_CHAINWALK: Invoke deadlock detection with a full
* walk of the lock chain.
*/
enum rtmutex_chainwalk {
RT_MUTEX_MIN_CHAINWALK,
RT_MUTEX_FULL_CHAINWALK,
};
/*
* PI-futex support (proxy locking functions, etc.):
*/
@ -111,12 +126,11 @@ extern void rt_mutex_proxy_unlock(struct rt_mutex *lock,
struct task_struct *proxy_owner);
extern int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter,
struct task_struct *task,
int detect_deadlock);
struct task_struct *task);
extern int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
struct hrtimer_sleeper *to,
struct rt_mutex_waiter *waiter,
int detect_deadlock);
struct rt_mutex_waiter *waiter);
extern int rt_mutex_timed_futex_lock(struct rt_mutex *l, struct hrtimer_sleeper *to);
#ifdef CONFIG_DEBUG_RT_MUTEXES
# include "rtmutex-debug.h"

4
kernel/locking/rwsem-xadd.c
View file

@ -329,7 +329,7 @@ bool rwsem_spin_on_owner(struct rw_semaphore *sem, struct task_struct *owner)
if (need_resched())
break;
arch_mutex_cpu_relax();
cpu_relax_lowlatency();
}
rcu_read_unlock();
@ -381,7 +381,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
* memory barriers as we'll eventually observe the right
* values at the cost of a few extra spins.
*/
arch_mutex_cpu_relax();
cpu_relax_lowlatency();
}
osq_unlock(&sem->osq);
done:

2
lib/Kconfig.debug
View file

@ -835,7 +835,7 @@ config DEBUG_RT_MUTEXES
config RT_MUTEX_TESTER
bool "Built-in scriptable tester for rt-mutexes"
depends on DEBUG_KERNEL && RT_MUTEXES
depends on DEBUG_KERNEL && RT_MUTEXES && BROKEN
help
This option enables a rt-mutex tester.

3
lib/lockref.c
View file

@ -1,6 +1,5 @@
#include <linux/export.h>
#include <linux/lockref.h>
#include <linux/mutex.h>
#if USE_CMPXCHG_LOCKREF
@ -29,7 +28,7 @@
if (likely(old.lock_count == prev.lock_count)) { \
SUCCESS; \
} \
arch_mutex_cpu_relax(); \
cpu_relax_lowlatency(); \
} \
} while (0)