linux/kernel/locking/rwsem.c
John Stultz 92cc5d00a4 locking/rwsem: Add __always_inline annotation to __down_read_common() and inlined callers
Apparently despite it being marked inline, the compiler
may not inline __down_read_common() which makes it difficult
to identify the cause of lock contention, as the blocked
function in traceevents will always be listed as
__down_read_common().

So this patch adds __always_inline annotation to the common
function (as well as the inlined helper callers) to force it to
be inlined so the blocking function will be listed (via Wchan)
in traceevents.

Fixes: c995e638cc ("locking/rwsem: Fold __down_{read,write}*()")
Reported-by: Tim Murray <timmurray@google.com>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20230503023351.2832796-1-jstultz@google.com
2023-05-08 10:58:24 +02:00

1717 lines
46 KiB
C

// SPDX-License-Identifier: GPL-2.0
/* kernel/rwsem.c: R/W semaphores, public implementation
*
* Written by David Howells (dhowells@redhat.com).
* Derived from asm-i386/semaphore.h
*
* Writer lock-stealing by Alex Shi <alex.shi@intel.com>
* and Michel Lespinasse <walken@google.com>
*
* Optimistic spinning by Tim Chen <tim.c.chen@intel.com>
* and Davidlohr Bueso <davidlohr@hp.com>. Based on mutexes.
*
* Rwsem count bit fields re-definition and rwsem rearchitecture by
* Waiman Long <longman@redhat.com> and
* Peter Zijlstra <peterz@infradead.org>.
*/
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/sched/rt.h>
#include <linux/sched/task.h>
#include <linux/sched/debug.h>
#include <linux/sched/wake_q.h>
#include <linux/sched/signal.h>
#include <linux/sched/clock.h>
#include <linux/export.h>
#include <linux/rwsem.h>
#include <linux/atomic.h>
#include <trace/events/lock.h>
#ifndef CONFIG_PREEMPT_RT
#include "lock_events.h"
/*
* The least significant 2 bits of the owner value has the following
* meanings when set.
* - Bit 0: RWSEM_READER_OWNED - The rwsem is owned by readers
* - Bit 1: RWSEM_NONSPINNABLE - Cannot spin on a reader-owned lock
*
* When the rwsem is reader-owned and a spinning writer has timed out,
* the nonspinnable bit will be set to disable optimistic spinning.
* When a writer acquires a rwsem, it puts its task_struct pointer
* into the owner field. It is cleared after an unlock.
*
* When a reader acquires a rwsem, it will also puts its task_struct
* pointer into the owner field with the RWSEM_READER_OWNED bit set.
* On unlock, the owner field will largely be left untouched. So
* for a free or reader-owned rwsem, the owner value may contain
* information about the last reader that acquires the rwsem.
*
* That information may be helpful in debugging cases where the system
* seems to hang on a reader owned rwsem especially if only one reader
* is involved. Ideally we would like to track all the readers that own
* a rwsem, but the overhead is simply too big.
*
* A fast path reader optimistic lock stealing is supported when the rwsem
* is previously owned by a writer and the following conditions are met:
* - rwsem is not currently writer owned
* - the handoff isn't set.
*/
#define RWSEM_READER_OWNED (1UL << 0)
#define RWSEM_NONSPINNABLE (1UL << 1)
#define RWSEM_OWNER_FLAGS_MASK (RWSEM_READER_OWNED | RWSEM_NONSPINNABLE)
#ifdef CONFIG_DEBUG_RWSEMS
# define DEBUG_RWSEMS_WARN_ON(c, sem) do { \
if (!debug_locks_silent && \
WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, magic = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
#c, atomic_long_read(&(sem)->count), \
(unsigned long) sem->magic, \
atomic_long_read(&(sem)->owner), (long)current, \
list_empty(&(sem)->wait_list) ? "" : "not ")) \
debug_locks_off(); \
} while (0)
#else
# define DEBUG_RWSEMS_WARN_ON(c, sem)
#endif
/*
* On 64-bit architectures, the bit definitions of the count are:
*
* Bit 0 - writer locked bit
* Bit 1 - waiters present bit
* Bit 2 - lock handoff bit
* Bits 3-7 - reserved
* Bits 8-62 - 55-bit reader count
* Bit 63 - read fail bit
*
* On 32-bit architectures, the bit definitions of the count are:
*
* Bit 0 - writer locked bit
* Bit 1 - waiters present bit
* Bit 2 - lock handoff bit
* Bits 3-7 - reserved
* Bits 8-30 - 23-bit reader count
* Bit 31 - read fail bit
*
* It is not likely that the most significant bit (read fail bit) will ever
* be set. This guard bit is still checked anyway in the down_read() fastpath
* just in case we need to use up more of the reader bits for other purpose
* in the future.
*
* atomic_long_fetch_add() is used to obtain reader lock, whereas
* atomic_long_cmpxchg() will be used to obtain writer lock.
*
* There are three places where the lock handoff bit may be set or cleared.
* 1) rwsem_mark_wake() for readers -- set, clear
* 2) rwsem_try_write_lock() for writers -- set, clear
* 3) rwsem_del_waiter() -- clear
*
* For all the above cases, wait_lock will be held. A writer must also
* be the first one in the wait_list to be eligible for setting the handoff
* bit. So concurrent setting/clearing of handoff bit is not possible.
*/
#define RWSEM_WRITER_LOCKED (1UL << 0)
#define RWSEM_FLAG_WAITERS (1UL << 1)
#define RWSEM_FLAG_HANDOFF (1UL << 2)
#define RWSEM_FLAG_READFAIL (1UL << (BITS_PER_LONG - 1))
#define RWSEM_READER_SHIFT 8
#define RWSEM_READER_BIAS (1UL << RWSEM_READER_SHIFT)
#define RWSEM_READER_MASK (~(RWSEM_READER_BIAS - 1))
#define RWSEM_WRITER_MASK RWSEM_WRITER_LOCKED
#define RWSEM_LOCK_MASK (RWSEM_WRITER_MASK|RWSEM_READER_MASK)
#define RWSEM_READ_FAILED_MASK (RWSEM_WRITER_MASK|RWSEM_FLAG_WAITERS|\
RWSEM_FLAG_HANDOFF|RWSEM_FLAG_READFAIL)
/*
* All writes to owner are protected by WRITE_ONCE() to make sure that
* store tearing can't happen as optimistic spinners may read and use
* the owner value concurrently without lock. Read from owner, however,
* may not need READ_ONCE() as long as the pointer value is only used
* for comparison and isn't being dereferenced.
*
* Both rwsem_{set,clear}_owner() functions should be in the same
* preempt disable section as the atomic op that changes sem->count.
*/
static inline void rwsem_set_owner(struct rw_semaphore *sem)
{
lockdep_assert_preemption_disabled();
atomic_long_set(&sem->owner, (long)current);
}
static inline void rwsem_clear_owner(struct rw_semaphore *sem)
{
lockdep_assert_preemption_disabled();
atomic_long_set(&sem->owner, 0);
}
/*
* Test the flags in the owner field.
*/
static inline bool rwsem_test_oflags(struct rw_semaphore *sem, long flags)
{
return atomic_long_read(&sem->owner) & flags;
}
/*
* The task_struct pointer of the last owning reader will be left in
* the owner field.
*
* Note that the owner value just indicates the task has owned the rwsem
* previously, it may not be the real owner or one of the real owners
* anymore when that field is examined, so take it with a grain of salt.
*
* The reader non-spinnable bit is preserved.
*/
static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
struct task_struct *owner)
{
unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED |
(atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE);
atomic_long_set(&sem->owner, val);
}
static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
{
__rwsem_set_reader_owned(sem, current);
}
/*
* Return true if the rwsem is owned by a reader.
*/
static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
{
#ifdef CONFIG_DEBUG_RWSEMS
/*
* Check the count to see if it is write-locked.
*/
long count = atomic_long_read(&sem->count);
if (count & RWSEM_WRITER_MASK)
return false;
#endif
return rwsem_test_oflags(sem, RWSEM_READER_OWNED);
}
#ifdef CONFIG_DEBUG_RWSEMS
/*
* With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there
* is a task pointer in owner of a reader-owned rwsem, it will be the
* real owner or one of the real owners. The only exception is when the
* unlock is done by up_read_non_owner().
*/
static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
{
unsigned long val = atomic_long_read(&sem->owner);
while ((val & ~RWSEM_OWNER_FLAGS_MASK) == (unsigned long)current) {
if (atomic_long_try_cmpxchg(&sem->owner, &val,
val & RWSEM_OWNER_FLAGS_MASK))
return;
}
}
#else
static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
{
}
#endif
/*
* Set the RWSEM_NONSPINNABLE bits if the RWSEM_READER_OWNED flag
* remains set. Otherwise, the operation will be aborted.
*/
static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
{
unsigned long owner = atomic_long_read(&sem->owner);
do {
if (!(owner & RWSEM_READER_OWNED))
break;
if (owner & RWSEM_NONSPINNABLE)
break;
} while (!atomic_long_try_cmpxchg(&sem->owner, &owner,
owner | RWSEM_NONSPINNABLE));
}
static inline bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp)
{
*cntp = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);
if (WARN_ON_ONCE(*cntp < 0))
rwsem_set_nonspinnable(sem);
if (!(*cntp & RWSEM_READ_FAILED_MASK)) {
rwsem_set_reader_owned(sem);
return true;
}
return false;
}
static inline bool rwsem_write_trylock(struct rw_semaphore *sem)
{
long tmp = RWSEM_UNLOCKED_VALUE;
if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, RWSEM_WRITER_LOCKED)) {
rwsem_set_owner(sem);
return true;
}
return false;
}
/*
* Return just the real task structure pointer of the owner
*/
static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
{
return (struct task_struct *)
(atomic_long_read(&sem->owner) & ~RWSEM_OWNER_FLAGS_MASK);
}
/*
* Return the real task structure pointer of the owner and the embedded
* flags in the owner. pflags must be non-NULL.
*/
static inline struct task_struct *
rwsem_owner_flags(struct rw_semaphore *sem, unsigned long *pflags)
{
unsigned long owner = atomic_long_read(&sem->owner);
*pflags = owner & RWSEM_OWNER_FLAGS_MASK;
return (struct task_struct *)(owner & ~RWSEM_OWNER_FLAGS_MASK);
}
/*
* Guide to the rw_semaphore's count field.
*
* When the RWSEM_WRITER_LOCKED bit in count is set, the lock is owned
* by a writer.
*
* The lock is owned by readers when
* (1) the RWSEM_WRITER_LOCKED isn't set in count,
* (2) some of the reader bits are set in count, and
* (3) the owner field has RWSEM_READ_OWNED bit set.
*
* Having some reader bits set is not enough to guarantee a readers owned
* lock as the readers may be in the process of backing out from the count
* and a writer has just released the lock. So another writer may steal
* the lock immediately after that.
*/
/*
* Initialize an rwsem:
*/
void __init_rwsem(struct rw_semaphore *sem, const char *name,
struct lock_class_key *key)
{
#ifdef CONFIG_DEBUG_LOCK_ALLOC
/*
* Make sure we are not reinitializing a held semaphore:
*/
debug_check_no_locks_freed((void *)sem, sizeof(*sem));
lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
#endif
#ifdef CONFIG_DEBUG_RWSEMS
sem->magic = sem;
#endif
atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
raw_spin_lock_init(&sem->wait_lock);
INIT_LIST_HEAD(&sem->wait_list);
atomic_long_set(&sem->owner, 0L);
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
osq_lock_init(&sem->osq);
#endif
}
EXPORT_SYMBOL(__init_rwsem);
enum rwsem_waiter_type {
RWSEM_WAITING_FOR_WRITE,
RWSEM_WAITING_FOR_READ
};
struct rwsem_waiter {
struct list_head list;
struct task_struct *task;
enum rwsem_waiter_type type;
unsigned long timeout;
bool handoff_set;
};
#define rwsem_first_waiter(sem) \
list_first_entry(&sem->wait_list, struct rwsem_waiter, list)
enum rwsem_wake_type {
RWSEM_WAKE_ANY, /* Wake whatever's at head of wait list */
RWSEM_WAKE_READERS, /* Wake readers only */
RWSEM_WAKE_READ_OWNED /* Waker thread holds the read lock */
};
/*
* The typical HZ value is either 250 or 1000. So set the minimum waiting
* time to at least 4ms or 1 jiffy (if it is higher than 4ms) in the wait
* queue before initiating the handoff protocol.
*/
#define RWSEM_WAIT_TIMEOUT DIV_ROUND_UP(HZ, 250)
/*
* Magic number to batch-wakeup waiting readers, even when writers are
* also present in the queue. This both limits the amount of work the
* waking thread must do and also prevents any potential counter overflow,
* however unlikely.
*/
#define MAX_READERS_WAKEUP 0x100
static inline void
rwsem_add_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter)
{
lockdep_assert_held(&sem->wait_lock);
list_add_tail(&waiter->list, &sem->wait_list);
/* caller will set RWSEM_FLAG_WAITERS */
}
/*
* Remove a waiter from the wait_list and clear flags.
*
* Both rwsem_mark_wake() and rwsem_try_write_lock() contain a full 'copy' of
* this function. Modify with care.
*
* Return: true if wait_list isn't empty and false otherwise
*/
static inline bool
rwsem_del_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter)
{
lockdep_assert_held(&sem->wait_lock);
list_del(&waiter->list);
if (likely(!list_empty(&sem->wait_list)))
return true;
atomic_long_andnot(RWSEM_FLAG_HANDOFF | RWSEM_FLAG_WAITERS, &sem->count);
return false;
}
/*
* handle the lock release when processes blocked on it that can now run
* - if we come here from up_xxxx(), then the RWSEM_FLAG_WAITERS bit must
* have been set.
* - there must be someone on the queue
* - the wait_lock must be held by the caller
* - tasks are marked for wakeup, the caller must later invoke wake_up_q()
* to actually wakeup the blocked task(s) and drop the reference count,
* preferably when the wait_lock is released
* - woken process blocks are discarded from the list after having task zeroed
* - writers are only marked woken if downgrading is false
*
* Implies rwsem_del_waiter() for all woken readers.
*/
static void rwsem_mark_wake(struct rw_semaphore *sem,
enum rwsem_wake_type wake_type,
struct wake_q_head *wake_q)
{
struct rwsem_waiter *waiter, *tmp;
long oldcount, woken = 0, adjustment = 0;
struct list_head wlist;
lockdep_assert_held(&sem->wait_lock);
/*
* Take a peek at the queue head waiter such that we can determine
* the wakeup(s) to perform.
*/
waiter = rwsem_first_waiter(sem);
if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
if (wake_type == RWSEM_WAKE_ANY) {
/*
* Mark writer at the front of the queue for wakeup.
* Until the task is actually later awoken later by
* the caller, other writers are able to steal it.
* Readers, on the other hand, will block as they
* will notice the queued writer.
*/
wake_q_add(wake_q, waiter->task);
lockevent_inc(rwsem_wake_writer);
}
return;
}
/*
* No reader wakeup if there are too many of them already.
*/
if (unlikely(atomic_long_read(&sem->count) < 0))
return;
/*
* Writers might steal the lock before we grant it to the next reader.
* We prefer to do the first reader grant before counting readers
* so we can bail out early if a writer stole the lock.
*/
if (wake_type != RWSEM_WAKE_READ_OWNED) {
struct task_struct *owner;
adjustment = RWSEM_READER_BIAS;
oldcount = atomic_long_fetch_add(adjustment, &sem->count);
if (unlikely(oldcount & RWSEM_WRITER_MASK)) {
/*
* When we've been waiting "too" long (for writers
* to give up the lock), request a HANDOFF to
* force the issue.
*/
if (time_after(jiffies, waiter->timeout)) {
if (!(oldcount & RWSEM_FLAG_HANDOFF)) {
adjustment -= RWSEM_FLAG_HANDOFF;
lockevent_inc(rwsem_rlock_handoff);
}
waiter->handoff_set = true;
}
atomic_long_add(-adjustment, &sem->count);
return;
}
/*
* Set it to reader-owned to give spinners an early
* indication that readers now have the lock.
* The reader nonspinnable bit seen at slowpath entry of
* the reader is copied over.
*/
owner = waiter->task;
__rwsem_set_reader_owned(sem, owner);
}
/*
* Grant up to MAX_READERS_WAKEUP read locks to all the readers in the
* queue. We know that the woken will be at least 1 as we accounted
* for above. Note we increment the 'active part' of the count by the
* number of readers before waking any processes up.
*
* This is an adaptation of the phase-fair R/W locks where at the
* reader phase (first waiter is a reader), all readers are eligible
* to acquire the lock at the same time irrespective of their order
* in the queue. The writers acquire the lock according to their
* order in the queue.
*
* We have to do wakeup in 2 passes to prevent the possibility that
* the reader count may be decremented before it is incremented. It
* is because the to-be-woken waiter may not have slept yet. So it
* may see waiter->task got cleared, finish its critical section and
* do an unlock before the reader count increment.
*
* 1) Collect the read-waiters in a separate list, count them and
* fully increment the reader count in rwsem.
* 2) For each waiters in the new list, clear waiter->task and
* put them into wake_q to be woken up later.
*/
INIT_LIST_HEAD(&wlist);
list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {
if (waiter->type == RWSEM_WAITING_FOR_WRITE)
continue;
woken++;
list_move_tail(&waiter->list, &wlist);
/*
* Limit # of readers that can be woken up per wakeup call.
*/
if (unlikely(woken >= MAX_READERS_WAKEUP))
break;
}
adjustment = woken * RWSEM_READER_BIAS - adjustment;
lockevent_cond_inc(rwsem_wake_reader, woken);
oldcount = atomic_long_read(&sem->count);
if (list_empty(&sem->wait_list)) {
/*
* Combined with list_move_tail() above, this implies
* rwsem_del_waiter().
*/
adjustment -= RWSEM_FLAG_WAITERS;
if (oldcount & RWSEM_FLAG_HANDOFF)
adjustment -= RWSEM_FLAG_HANDOFF;
} else if (woken) {
/*
* When we've woken a reader, we no longer need to force
* writers to give up the lock and we can clear HANDOFF.
*/
if (oldcount & RWSEM_FLAG_HANDOFF)
adjustment -= RWSEM_FLAG_HANDOFF;
}
if (adjustment)
atomic_long_add(adjustment, &sem->count);
/* 2nd pass */
list_for_each_entry_safe(waiter, tmp, &wlist, list) {
struct task_struct *tsk;
tsk = waiter->task;
get_task_struct(tsk);
/*
* Ensure calling get_task_struct() before setting the reader
* waiter to nil such that rwsem_down_read_slowpath() cannot
* race with do_exit() by always holding a reference count
* to the task to wakeup.
*/
smp_store_release(&waiter->task, NULL);
/*
* Ensure issuing the wakeup (either by us or someone else)
* after setting the reader waiter to nil.
*/
wake_q_add_safe(wake_q, tsk);
}
}
/*
* Remove a waiter and try to wake up other waiters in the wait queue
* This function is called from the out_nolock path of both the reader and
* writer slowpaths with wait_lock held. It releases the wait_lock and
* optionally wake up waiters before it returns.
*/
static inline void
rwsem_del_wake_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter,
struct wake_q_head *wake_q)
__releases(&sem->wait_lock)
{
bool first = rwsem_first_waiter(sem) == waiter;
wake_q_init(wake_q);
/*
* If the wait_list isn't empty and the waiter to be deleted is
* the first waiter, we wake up the remaining waiters as they may
* be eligible to acquire or spin on the lock.
*/
if (rwsem_del_waiter(sem, waiter) && first)
rwsem_mark_wake(sem, RWSEM_WAKE_ANY, wake_q);
raw_spin_unlock_irq(&sem->wait_lock);
if (!wake_q_empty(wake_q))
wake_up_q(wake_q);
}
/*
* This function must be called with the sem->wait_lock held to prevent
* race conditions between checking the rwsem wait list and setting the
* sem->count accordingly.
*
* Implies rwsem_del_waiter() on success.
*/
static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
struct rwsem_waiter *waiter)
{
struct rwsem_waiter *first = rwsem_first_waiter(sem);
long count, new;
lockdep_assert_held(&sem->wait_lock);
count = atomic_long_read(&sem->count);
do {
bool has_handoff = !!(count & RWSEM_FLAG_HANDOFF);
if (has_handoff) {
/*
* Honor handoff bit and yield only when the first
* waiter is the one that set it. Otherwisee, we
* still try to acquire the rwsem.
*/
if (first->handoff_set && (waiter != first))
return false;
}
new = count;
if (count & RWSEM_LOCK_MASK) {
/*
* A waiter (first or not) can set the handoff bit
* if it is an RT task or wait in the wait queue
* for too long.
*/
if (has_handoff || (!rt_task(waiter->task) &&
!time_after(jiffies, waiter->timeout)))
return false;
new |= RWSEM_FLAG_HANDOFF;
} else {
new |= RWSEM_WRITER_LOCKED;
new &= ~RWSEM_FLAG_HANDOFF;
if (list_is_singular(&sem->wait_list))
new &= ~RWSEM_FLAG_WAITERS;
}
} while (!atomic_long_try_cmpxchg_acquire(&sem->count, &count, new));
/*
* We have either acquired the lock with handoff bit cleared or set
* the handoff bit. Only the first waiter can have its handoff_set
* set here to enable optimistic spinning in slowpath loop.
*/
if (new & RWSEM_FLAG_HANDOFF) {
first->handoff_set = true;
lockevent_inc(rwsem_wlock_handoff);
return false;
}
/*
* Have rwsem_try_write_lock() fully imply rwsem_del_waiter() on
* success.
*/
list_del(&waiter->list);
rwsem_set_owner(sem);
return true;
}
/*
* The rwsem_spin_on_owner() function returns the following 4 values
* depending on the lock owner state.
* OWNER_NULL : owner is currently NULL
* OWNER_WRITER: when owner changes and is a writer
* OWNER_READER: when owner changes and the new owner may be a reader.
* OWNER_NONSPINNABLE:
* when optimistic spinning has to stop because either the
* owner stops running, is unknown, or its timeslice has
* been used up.
*/
enum owner_state {
OWNER_NULL = 1 << 0,
OWNER_WRITER = 1 << 1,
OWNER_READER = 1 << 2,
OWNER_NONSPINNABLE = 1 << 3,
};
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
/*
* Try to acquire write lock before the writer has been put on wait queue.
*/
static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
{
long count = atomic_long_read(&sem->count);
while (!(count & (RWSEM_LOCK_MASK|RWSEM_FLAG_HANDOFF))) {
if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,
count | RWSEM_WRITER_LOCKED)) {
rwsem_set_owner(sem);
lockevent_inc(rwsem_opt_lock);
return true;
}
}
return false;
}
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
{
struct task_struct *owner;
unsigned long flags;
bool ret = true;
if (need_resched()) {
lockevent_inc(rwsem_opt_fail);
return false;
}
/*
* Disable preemption is equal to the RCU read-side crital section,
* thus the task_strcut structure won't go away.
*/
owner = rwsem_owner_flags(sem, &flags);
/*
* Don't check the read-owner as the entry may be stale.
*/
if ((flags & RWSEM_NONSPINNABLE) ||
(owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner)))
ret = false;
lockevent_cond_inc(rwsem_opt_fail, !ret);
return ret;
}
#define OWNER_SPINNABLE (OWNER_NULL | OWNER_WRITER | OWNER_READER)
static inline enum owner_state
rwsem_owner_state(struct task_struct *owner, unsigned long flags)
{
if (flags & RWSEM_NONSPINNABLE)
return OWNER_NONSPINNABLE;
if (flags & RWSEM_READER_OWNED)
return OWNER_READER;
return owner ? OWNER_WRITER : OWNER_NULL;
}
static noinline enum owner_state
rwsem_spin_on_owner(struct rw_semaphore *sem)
{
struct task_struct *new, *owner;
unsigned long flags, new_flags;
enum owner_state state;
lockdep_assert_preemption_disabled();
owner = rwsem_owner_flags(sem, &flags);
state = rwsem_owner_state(owner, flags);
if (state != OWNER_WRITER)
return state;
for (;;) {
/*
* When a waiting writer set the handoff flag, it may spin
* on the owner as well. Once that writer acquires the lock,
* we can spin on it. So we don't need to quit even when the
* handoff bit is set.
*/
new = rwsem_owner_flags(sem, &new_flags);
if ((new != owner) || (new_flags != flags)) {
state = rwsem_owner_state(new, new_flags);
break;
}
/*
* Ensure we emit the owner->on_cpu, dereference _after_
* checking sem->owner still matches owner, if that fails,
* owner might point to free()d memory, if it still matches,
* our spinning context already disabled preemption which is
* equal to RCU read-side crital section ensures the memory
* stays valid.
*/
barrier();
if (need_resched() || !owner_on_cpu(owner)) {
state = OWNER_NONSPINNABLE;
break;
}
cpu_relax();
}
return state;
}
/*
* Calculate reader-owned rwsem spinning threshold for writer
*
* The more readers own the rwsem, the longer it will take for them to
* wind down and free the rwsem. So the empirical formula used to
* determine the actual spinning time limit here is:
*
* Spinning threshold = (10 + nr_readers/2)us
*
* The limit is capped to a maximum of 25us (30 readers). This is just
* a heuristic and is subjected to change in the future.
*/
static inline u64 rwsem_rspin_threshold(struct rw_semaphore *sem)
{
long count = atomic_long_read(&sem->count);
int readers = count >> RWSEM_READER_SHIFT;
u64 delta;
if (readers > 30)
readers = 30;
delta = (20 + readers) * NSEC_PER_USEC / 2;
return sched_clock() + delta;
}
static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
{
bool taken = false;
int prev_owner_state = OWNER_NULL;
int loop = 0;
u64 rspin_threshold = 0;
/* sem->wait_lock should not be held when doing optimistic spinning */
if (!osq_lock(&sem->osq))
goto done;
/*
* Optimistically spin on the owner field and attempt to acquire the
* lock whenever the owner changes. Spinning will be stopped when:
* 1) the owning writer isn't running; or
* 2) readers own the lock and spinning time has exceeded limit.
*/
for (;;) {
enum owner_state owner_state;
owner_state = rwsem_spin_on_owner(sem);
if (!(owner_state & OWNER_SPINNABLE))
break;
/*
* Try to acquire the lock
*/
taken = rwsem_try_write_lock_unqueued(sem);
if (taken)
break;
/*
* Time-based reader-owned rwsem optimistic spinning
*/
if (owner_state == OWNER_READER) {
/*
* Re-initialize rspin_threshold every time when
* the owner state changes from non-reader to reader.
* This allows a writer to steal the lock in between
* 2 reader phases and have the threshold reset at
* the beginning of the 2nd reader phase.
*/
if (prev_owner_state != OWNER_READER) {
if (rwsem_test_oflags(sem, RWSEM_NONSPINNABLE))
break;
rspin_threshold = rwsem_rspin_threshold(sem);
loop = 0;
}
/*
* Check time threshold once every 16 iterations to
* avoid calling sched_clock() too frequently so
* as to reduce the average latency between the times
* when the lock becomes free and when the spinner
* is ready to do a trylock.
*/
else if (!(++loop & 0xf) && (sched_clock() > rspin_threshold)) {
rwsem_set_nonspinnable(sem);
lockevent_inc(rwsem_opt_nospin);
break;
}
}
/*
* An RT task cannot do optimistic spinning if it cannot
* be sure the lock holder is running or live-lock may
* happen if the current task and the lock holder happen
* to run in the same CPU. However, aborting optimistic
* spinning while a NULL owner is detected may miss some
* opportunity where spinning can continue without causing
* problem.
*
* There are 2 possible cases where an RT task may be able
* to continue spinning.
*
* 1) The lock owner is in the process of releasing the
* lock, sem->owner is cleared but the lock has not
* been released yet.
* 2) The lock was free and owner cleared, but another
* task just comes in and acquire the lock before
* we try to get it. The new owner may be a spinnable
* writer.
*
* To take advantage of two scenarios listed above, the RT
* task is made to retry one more time to see if it can
* acquire the lock or continue spinning on the new owning
* writer. Of course, if the time lag is long enough or the
* new owner is not a writer or spinnable, the RT task will
* quit spinning.
*
* If the owner is a writer, the need_resched() check is
* done inside rwsem_spin_on_owner(). If the owner is not
* a writer, need_resched() check needs to be done here.
*/
if (owner_state != OWNER_WRITER) {
if (need_resched())
break;
if (rt_task(current) &&
(prev_owner_state != OWNER_WRITER))
break;
}
prev_owner_state = owner_state;
/*
* The cpu_relax() call is a compiler barrier which forces
* everything in this loop to be re-loaded. We don't need
* memory barriers as we'll eventually observe the right
* values at the cost of a few extra spins.
*/
cpu_relax();
}
osq_unlock(&sem->osq);
done:
lockevent_cond_inc(rwsem_opt_fail, !taken);
return taken;
}
/*
* Clear the owner's RWSEM_NONSPINNABLE bit if it is set. This should
* only be called when the reader count reaches 0.
*/
static inline void clear_nonspinnable(struct rw_semaphore *sem)
{
if (unlikely(rwsem_test_oflags(sem, RWSEM_NONSPINNABLE)))
atomic_long_andnot(RWSEM_NONSPINNABLE, &sem->owner);
}
#else
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
{
return false;
}
static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem)
{
return false;
}
static inline void clear_nonspinnable(struct rw_semaphore *sem) { }
static inline enum owner_state
rwsem_spin_on_owner(struct rw_semaphore *sem)
{
return OWNER_NONSPINNABLE;
}
#endif
/*
* Prepare to wake up waiter(s) in the wait queue by putting them into the
* given wake_q if the rwsem lock owner isn't a writer. If rwsem is likely
* reader-owned, wake up read lock waiters in queue front or wake up any
* front waiter otherwise.
* This is being called from both reader and writer slow paths.
*/
static inline void rwsem_cond_wake_waiter(struct rw_semaphore *sem, long count,
struct wake_q_head *wake_q)
{
enum rwsem_wake_type wake_type;
if (count & RWSEM_WRITER_MASK)
return;
if (count & RWSEM_READER_MASK) {
wake_type = RWSEM_WAKE_READERS;
} else {
wake_type = RWSEM_WAKE_ANY;
clear_nonspinnable(sem);
}
rwsem_mark_wake(sem, wake_type, wake_q);
}
/*
* Wait for the read lock to be granted
*/
static struct rw_semaphore __sched *
rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int state)
{
long adjustment = -RWSEM_READER_BIAS;
long rcnt = (count >> RWSEM_READER_SHIFT);
struct rwsem_waiter waiter;
DEFINE_WAKE_Q(wake_q);
/*
* To prevent a constant stream of readers from starving a sleeping
* waiter, don't attempt optimistic lock stealing if the lock is
* currently owned by readers.
*/
if ((atomic_long_read(&sem->owner) & RWSEM_READER_OWNED) &&
(rcnt > 1) && !(count & RWSEM_WRITER_LOCKED))
goto queue;
/*
* Reader optimistic lock stealing.
*/
if (!(count & (RWSEM_WRITER_LOCKED | RWSEM_FLAG_HANDOFF))) {
rwsem_set_reader_owned(sem);
lockevent_inc(rwsem_rlock_steal);
/*
* Wake up other readers in the wait queue if it is
* the first reader.
*/
if ((rcnt == 1) && (count & RWSEM_FLAG_WAITERS)) {
raw_spin_lock_irq(&sem->wait_lock);
if (!list_empty(&sem->wait_list))
rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED,
&wake_q);
raw_spin_unlock_irq(&sem->wait_lock);
wake_up_q(&wake_q);
}
return sem;
}
queue:
waiter.task = current;
waiter.type = RWSEM_WAITING_FOR_READ;
waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
waiter.handoff_set = false;
raw_spin_lock_irq(&sem->wait_lock);
if (list_empty(&sem->wait_list)) {
/*
* In case the wait queue is empty and the lock isn't owned
* by a writer, this reader can exit the slowpath and return
* immediately as its RWSEM_READER_BIAS has already been set
* in the count.
*/
if (!(atomic_long_read(&sem->count) & RWSEM_WRITER_MASK)) {
/* Provide lock ACQUIRE */
smp_acquire__after_ctrl_dep();
raw_spin_unlock_irq(&sem->wait_lock);
rwsem_set_reader_owned(sem);
lockevent_inc(rwsem_rlock_fast);
return sem;
}
adjustment += RWSEM_FLAG_WAITERS;
}
rwsem_add_waiter(sem, &waiter);
/* we're now waiting on the lock, but no longer actively locking */
count = atomic_long_add_return(adjustment, &sem->count);
rwsem_cond_wake_waiter(sem, count, &wake_q);
raw_spin_unlock_irq(&sem->wait_lock);
if (!wake_q_empty(&wake_q))
wake_up_q(&wake_q);
trace_contention_begin(sem, LCB_F_READ);
/* wait to be given the lock */
for (;;) {
set_current_state(state);
if (!smp_load_acquire(&waiter.task)) {
/* Matches rwsem_mark_wake()'s smp_store_release(). */
break;
}
if (signal_pending_state(state, current)) {
raw_spin_lock_irq(&sem->wait_lock);
if (waiter.task)
goto out_nolock;
raw_spin_unlock_irq(&sem->wait_lock);
/* Ordered by sem->wait_lock against rwsem_mark_wake(). */
break;
}
schedule_preempt_disabled();
lockevent_inc(rwsem_sleep_reader);
}
__set_current_state(TASK_RUNNING);
lockevent_inc(rwsem_rlock);
trace_contention_end(sem, 0);
return sem;
out_nolock:
rwsem_del_wake_waiter(sem, &waiter, &wake_q);
__set_current_state(TASK_RUNNING);
lockevent_inc(rwsem_rlock_fail);
trace_contention_end(sem, -EINTR);
return ERR_PTR(-EINTR);
}
/*
* Wait until we successfully acquire the write lock
*/
static struct rw_semaphore __sched *
rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
{
struct rwsem_waiter waiter;
DEFINE_WAKE_Q(wake_q);
/* do optimistic spinning and steal lock if possible */
if (rwsem_can_spin_on_owner(sem) && rwsem_optimistic_spin(sem)) {
/* rwsem_optimistic_spin() implies ACQUIRE on success */
return sem;
}
/*
* Optimistic spinning failed, proceed to the slowpath
* and block until we can acquire the sem.
*/
waiter.task = current;
waiter.type = RWSEM_WAITING_FOR_WRITE;
waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
waiter.handoff_set = false;
raw_spin_lock_irq(&sem->wait_lock);
rwsem_add_waiter(sem, &waiter);
/* we're now waiting on the lock */
if (rwsem_first_waiter(sem) != &waiter) {
rwsem_cond_wake_waiter(sem, atomic_long_read(&sem->count),
&wake_q);
if (!wake_q_empty(&wake_q)) {
/*
* We want to minimize wait_lock hold time especially
* when a large number of readers are to be woken up.
*/
raw_spin_unlock_irq(&sem->wait_lock);
wake_up_q(&wake_q);
raw_spin_lock_irq(&sem->wait_lock);
}
} else {
atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count);
}
/* wait until we successfully acquire the lock */
set_current_state(state);
trace_contention_begin(sem, LCB_F_WRITE);
for (;;) {
if (rwsem_try_write_lock(sem, &waiter)) {
/* rwsem_try_write_lock() implies ACQUIRE on success */
break;
}
raw_spin_unlock_irq(&sem->wait_lock);
if (signal_pending_state(state, current))
goto out_nolock;
/*
* After setting the handoff bit and failing to acquire
* the lock, attempt to spin on owner to accelerate lock
* transfer. If the previous owner is a on-cpu writer and it
* has just released the lock, OWNER_NULL will be returned.
* In this case, we attempt to acquire the lock again
* without sleeping.
*/
if (waiter.handoff_set) {
enum owner_state owner_state;
owner_state = rwsem_spin_on_owner(sem);
if (owner_state == OWNER_NULL)
goto trylock_again;
}
schedule_preempt_disabled();
lockevent_inc(rwsem_sleep_writer);
set_current_state(state);
trylock_again:
raw_spin_lock_irq(&sem->wait_lock);
}
__set_current_state(TASK_RUNNING);
raw_spin_unlock_irq(&sem->wait_lock);
lockevent_inc(rwsem_wlock);
trace_contention_end(sem, 0);
return sem;
out_nolock:
__set_current_state(TASK_RUNNING);
raw_spin_lock_irq(&sem->wait_lock);
rwsem_del_wake_waiter(sem, &waiter, &wake_q);
lockevent_inc(rwsem_wlock_fail);
trace_contention_end(sem, -EINTR);
return ERR_PTR(-EINTR);
}
/*
* handle waking up a waiter on the semaphore
* - up_read/up_write has decremented the active part of count if we come here
*/
static struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem)
{
unsigned long flags;
DEFINE_WAKE_Q(wake_q);
raw_spin_lock_irqsave(&sem->wait_lock, flags);
if (!list_empty(&sem->wait_list))
rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
wake_up_q(&wake_q);
return sem;
}
/*
* downgrade a write lock into a read lock
* - caller incremented waiting part of count and discovered it still negative
* - just wake up any readers at the front of the queue
*/
static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
{
unsigned long flags;
DEFINE_WAKE_Q(wake_q);
raw_spin_lock_irqsave(&sem->wait_lock, flags);
if (!list_empty(&sem->wait_list))
rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
wake_up_q(&wake_q);
return sem;
}
/*
* lock for reading
*/
static __always_inline int __down_read_common(struct rw_semaphore *sem, int state)
{
int ret = 0;
long count;
preempt_disable();
if (!rwsem_read_trylock(sem, &count)) {
if (IS_ERR(rwsem_down_read_slowpath(sem, count, state))) {
ret = -EINTR;
goto out;
}
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
}
out:
preempt_enable();
return ret;
}
static __always_inline void __down_read(struct rw_semaphore *sem)
{
__down_read_common(sem, TASK_UNINTERRUPTIBLE);
}
static __always_inline int __down_read_interruptible(struct rw_semaphore *sem)
{
return __down_read_common(sem, TASK_INTERRUPTIBLE);
}
static __always_inline int __down_read_killable(struct rw_semaphore *sem)
{
return __down_read_common(sem, TASK_KILLABLE);
}
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
int ret = 0;
long tmp;
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
preempt_disable();
tmp = atomic_long_read(&sem->count);
while (!(tmp & RWSEM_READ_FAILED_MASK)) {
if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
tmp + RWSEM_READER_BIAS)) {
rwsem_set_reader_owned(sem);
ret = 1;
break;
}
}
preempt_enable();
return ret;
}
/*
* lock for writing
*/
static inline int __down_write_common(struct rw_semaphore *sem, int state)
{
int ret = 0;
preempt_disable();
if (unlikely(!rwsem_write_trylock(sem))) {
if (IS_ERR(rwsem_down_write_slowpath(sem, state)))
ret = -EINTR;
}
preempt_enable();
return ret;
}
static inline void __down_write(struct rw_semaphore *sem)
{
__down_write_common(sem, TASK_UNINTERRUPTIBLE);
}
static inline int __down_write_killable(struct rw_semaphore *sem)
{
return __down_write_common(sem, TASK_KILLABLE);
}
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
int ret;
preempt_disable();
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
ret = rwsem_write_trylock(sem);
preempt_enable();
return ret;
}
/*
* unlock after reading
*/
static inline void __up_read(struct rw_semaphore *sem)
{
long tmp;
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
preempt_disable();
rwsem_clear_reader_owned(sem);
tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);
DEBUG_RWSEMS_WARN_ON(tmp < 0, sem);
if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) ==
RWSEM_FLAG_WAITERS)) {
clear_nonspinnable(sem);
rwsem_wake(sem);
}
preempt_enable();
}
/*
* unlock after writing
*/
static inline void __up_write(struct rw_semaphore *sem)
{
long tmp;
DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);
/*
* sem->owner may differ from current if the ownership is transferred
* to an anonymous writer by setting the RWSEM_NONSPINNABLE bits.
*/
DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) &&
!rwsem_test_oflags(sem, RWSEM_NONSPINNABLE), sem);
preempt_disable();
rwsem_clear_owner(sem);
tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count);
if (unlikely(tmp & RWSEM_FLAG_WAITERS))
rwsem_wake(sem);
preempt_enable();
}
/*
* downgrade write lock to read lock
*/
static inline void __downgrade_write(struct rw_semaphore *sem)
{
long tmp;
/*
* When downgrading from exclusive to shared ownership,
* anything inside the write-locked region cannot leak
* into the read side. In contrast, anything in the
* read-locked region is ok to be re-ordered into the
* write side. As such, rely on RELEASE semantics.
*/
DEBUG_RWSEMS_WARN_ON(rwsem_owner(sem) != current, sem);
preempt_disable();
tmp = atomic_long_fetch_add_release(
-RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count);
rwsem_set_reader_owned(sem);
if (tmp & RWSEM_FLAG_WAITERS)
rwsem_downgrade_wake(sem);
preempt_enable();
}
#else /* !CONFIG_PREEMPT_RT */
#define RT_MUTEX_BUILD_MUTEX
#include "rtmutex.c"
#define rwbase_set_and_save_current_state(state) \
set_current_state(state)
#define rwbase_restore_current_state() \
__set_current_state(TASK_RUNNING)
#define rwbase_rtmutex_lock_state(rtm, state) \
__rt_mutex_lock(rtm, state)
#define rwbase_rtmutex_slowlock_locked(rtm, state) \
__rt_mutex_slowlock_locked(rtm, NULL, state)
#define rwbase_rtmutex_unlock(rtm) \
__rt_mutex_unlock(rtm)
#define rwbase_rtmutex_trylock(rtm) \
__rt_mutex_trylock(rtm)
#define rwbase_signal_pending_state(state, current) \
signal_pending_state(state, current)
#define rwbase_schedule() \
schedule()
#include "rwbase_rt.c"
void __init_rwsem(struct rw_semaphore *sem, const char *name,
struct lock_class_key *key)
{
init_rwbase_rt(&(sem)->rwbase);
#ifdef CONFIG_DEBUG_LOCK_ALLOC
debug_check_no_locks_freed((void *)sem, sizeof(*sem));
lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);
#endif
}
EXPORT_SYMBOL(__init_rwsem);
static inline void __down_read(struct rw_semaphore *sem)
{
rwbase_read_lock(&sem->rwbase, TASK_UNINTERRUPTIBLE);
}
static inline int __down_read_interruptible(struct rw_semaphore *sem)
{
return rwbase_read_lock(&sem->rwbase, TASK_INTERRUPTIBLE);
}
static inline int __down_read_killable(struct rw_semaphore *sem)
{
return rwbase_read_lock(&sem->rwbase, TASK_KILLABLE);
}
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
return rwbase_read_trylock(&sem->rwbase);
}
static inline void __up_read(struct rw_semaphore *sem)
{
rwbase_read_unlock(&sem->rwbase, TASK_NORMAL);
}
static inline void __sched __down_write(struct rw_semaphore *sem)
{
rwbase_write_lock(&sem->rwbase, TASK_UNINTERRUPTIBLE);
}
static inline int __sched __down_write_killable(struct rw_semaphore *sem)
{
return rwbase_write_lock(&sem->rwbase, TASK_KILLABLE);
}
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
return rwbase_write_trylock(&sem->rwbase);
}
static inline void __up_write(struct rw_semaphore *sem)
{
rwbase_write_unlock(&sem->rwbase);
}
static inline void __downgrade_write(struct rw_semaphore *sem)
{
rwbase_write_downgrade(&sem->rwbase);
}
/* Debug stubs for the common API */
#define DEBUG_RWSEMS_WARN_ON(c, sem)
static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
struct task_struct *owner)
{
}
static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
{
int count = atomic_read(&sem->rwbase.readers);
return count < 0 && count != READER_BIAS;
}
#endif /* CONFIG_PREEMPT_RT */
/*
* lock for reading
*/
void __sched down_read(struct rw_semaphore *sem)
{
might_sleep();
rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
}
EXPORT_SYMBOL(down_read);
int __sched down_read_interruptible(struct rw_semaphore *sem)
{
might_sleep();
rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) {
rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
return 0;
}
EXPORT_SYMBOL(down_read_interruptible);
int __sched down_read_killable(struct rw_semaphore *sem)
{
might_sleep();
rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
return 0;
}
EXPORT_SYMBOL(down_read_killable);
/*
* trylock for reading -- returns 1 if successful, 0 if contention
*/
int down_read_trylock(struct rw_semaphore *sem)
{
int ret = __down_read_trylock(sem);
if (ret == 1)
rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
return ret;
}
EXPORT_SYMBOL(down_read_trylock);
/*
* lock for writing
*/
void __sched down_write(struct rw_semaphore *sem)
{
might_sleep();
rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
}
EXPORT_SYMBOL(down_write);
/*
* lock for writing
*/
int __sched down_write_killable(struct rw_semaphore *sem)
{
might_sleep();
rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
__down_write_killable)) {
rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
return 0;
}
EXPORT_SYMBOL(down_write_killable);
/*
* trylock for writing -- returns 1 if successful, 0 if contention
*/
int down_write_trylock(struct rw_semaphore *sem)
{
int ret = __down_write_trylock(sem);
if (ret == 1)
rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
return ret;
}
EXPORT_SYMBOL(down_write_trylock);
/*
* release a read lock
*/
void up_read(struct rw_semaphore *sem)
{
rwsem_release(&sem->dep_map, _RET_IP_);
__up_read(sem);
}
EXPORT_SYMBOL(up_read);
/*
* release a write lock
*/
void up_write(struct rw_semaphore *sem)
{
rwsem_release(&sem->dep_map, _RET_IP_);
__up_write(sem);
}
EXPORT_SYMBOL(up_write);
/*
* downgrade write lock to read lock
*/
void downgrade_write(struct rw_semaphore *sem)
{
lock_downgrade(&sem->dep_map, _RET_IP_);
__downgrade_write(sem);
}
EXPORT_SYMBOL(downgrade_write);
#ifdef CONFIG_DEBUG_LOCK_ALLOC
void down_read_nested(struct rw_semaphore *sem, int subclass)
{
might_sleep();
rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
}
EXPORT_SYMBOL(down_read_nested);
int down_read_killable_nested(struct rw_semaphore *sem, int subclass)
{
might_sleep();
rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
return 0;
}
EXPORT_SYMBOL(down_read_killable_nested);
void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
{
might_sleep();
rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
}
EXPORT_SYMBOL(_down_write_nest_lock);
void down_read_non_owner(struct rw_semaphore *sem)
{
might_sleep();
__down_read(sem);
/*
* The owner value for a reader-owned lock is mostly for debugging
* purpose only and is not critical to the correct functioning of
* rwsem. So it is perfectly fine to set it in a preempt-enabled
* context here.
*/
__rwsem_set_reader_owned(sem, NULL);
}
EXPORT_SYMBOL(down_read_non_owner);
void down_write_nested(struct rw_semaphore *sem, int subclass)
{
might_sleep();
rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
}
EXPORT_SYMBOL(down_write_nested);
int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
{
might_sleep();
rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
__down_write_killable)) {
rwsem_release(&sem->dep_map, _RET_IP_);
return -EINTR;
}
return 0;
}
EXPORT_SYMBOL(down_write_killable_nested);
void up_read_non_owner(struct rw_semaphore *sem)
{
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
__up_read(sem);
}
EXPORT_SYMBOL(up_read_non_owner);
#endif