linux/include/asm-parisc/spinlock.h
James Bottomley 08dc2ca61e [PARISC] Fix our spinlock implementation
We actually have two separate bad bugs

1. The read_lock implementation spins with disabled interrupts.  This is
completely wrong
2. Our spin_lock_irqsave should check to see if interrupts were enabled
before the call and re-enable interrupts around the inner spin loop.

The problem is that if we spin with interrupts off, we can't receive
IPIs. This has resulted in a bug where SMP machines suddenly spit
smp_call_function timeout messages and hang.

The scenario I've caught is

CPU0 does a flush_tlb_all holding the vmlist_lock for write.
CPU1 tries a cat of /proc/meminfo which tries to acquire vmlist_lock for
     read
CPU1 is now spinning with interrupts disabled
CPU0 tries to execute a smp_call_function to flush the local tlb caches

This is now a deadlock because CPU1 is spinning with interrupts disabled
and can never receive the IPI

Signed-off-by: James Bottomley <jejb@parisc-linux.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>
2005-11-17 16:35:09 -05:00

148 lines
3.1 KiB
C

#ifndef __ASM_SPINLOCK_H
#define __ASM_SPINLOCK_H
#include <asm/system.h>
#include <asm/processor.h>
#include <asm/spinlock_types.h>
static inline int __raw_spin_is_locked(raw_spinlock_t *x)
{
volatile unsigned int *a = __ldcw_align(x);
return *a == 0;
}
#define __raw_spin_lock(lock) __raw_spin_lock_flags(lock, 0)
#define __raw_spin_unlock_wait(x) \
do { cpu_relax(); } while (__raw_spin_is_locked(x))
static inline void __raw_spin_lock_flags(raw_spinlock_t *x,
unsigned long flags)
{
volatile unsigned int *a;
mb();
a = __ldcw_align(x);
while (__ldcw(a) == 0)
while (*a == 0)
if (flags & PSW_SM_I) {
local_irq_enable();
cpu_relax();
local_irq_disable();
} else
cpu_relax();
mb();
}
static inline void __raw_spin_unlock(raw_spinlock_t *x)
{
volatile unsigned int *a;
mb();
a = __ldcw_align(x);
*a = 1;
mb();
}
static inline int __raw_spin_trylock(raw_spinlock_t *x)
{
volatile unsigned int *a;
int ret;
mb();
a = __ldcw_align(x);
ret = __ldcw(a) != 0;
mb();
return ret;
}
/*
* Read-write spinlocks, allowing multiple readers
* but only one writer.
*/
#define __raw_read_trylock(lock) generic__raw_read_trylock(lock)
/* read_lock, read_unlock are pretty straightforward. Of course it somehow
* sucks we end up saving/restoring flags twice for read_lock_irqsave aso. */
static __inline__ void __raw_read_lock(raw_rwlock_t *rw)
{
__raw_spin_lock(&rw->lock);
rw->counter++;
__raw_spin_unlock(&rw->lock);
}
static __inline__ void __raw_read_unlock(raw_rwlock_t *rw)
{
__raw_spin_lock(&rw->lock);
rw->counter--;
__raw_spin_unlock(&rw->lock);
}
/* write_lock is less trivial. We optimistically grab the lock and check
* if we surprised any readers. If so we release the lock and wait till
* they're all gone before trying again
*
* Also note that we don't use the _irqsave / _irqrestore suffixes here.
* If we're called with interrupts enabled and we've got readers (or other
* writers) in interrupt handlers someone fucked up and we'd dead-lock
* sooner or later anyway. prumpf */
static __inline__ void __raw_write_lock(raw_rwlock_t *rw)
{
retry:
__raw_spin_lock(&rw->lock);
if(rw->counter != 0) {
/* this basically never happens */
__raw_spin_unlock(&rw->lock);
while (rw->counter != 0)
cpu_relax();
goto retry;
}
/* got it. now leave without unlocking */
rw->counter = -1; /* remember we are locked */
}
/* write_unlock is absolutely trivial - we don't have to wait for anything */
static __inline__ void __raw_write_unlock(raw_rwlock_t *rw)
{
rw->counter = 0;
__raw_spin_unlock(&rw->lock);
}
static __inline__ int __raw_write_trylock(raw_rwlock_t *rw)
{
__raw_spin_lock(&rw->lock);
if (rw->counter != 0) {
/* this basically never happens */
__raw_spin_unlock(&rw->lock);
return 0;
}
/* got it. now leave without unlocking */
rw->counter = -1; /* remember we are locked */
return 1;
}
static __inline__ int __raw_is_read_locked(raw_rwlock_t *rw)
{
return rw->counter > 0;
}
static __inline__ int __raw_is_write_locked(raw_rwlock_t *rw)
{
return rw->counter < 0;
}
#endif /* __ASM_SPINLOCK_H */