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[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>
This commit is contained in:
James Bottomley 2005-11-17 16:35:09 -05:00 committed by Kyle McMartin
parent 4269b0d371
commit 08dc2ca61e
1 changed files with 10 additions and 9 deletions
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19
include/asm-parisc/spinlock.h
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@ -11,18 +11,25 @@ static inline int __raw_spin_is_locked(raw_spinlock_t *x)
return *a == 0; return *a == 0;
} }
#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock) #define __raw_spin_lock(lock) __raw_spin_lock_flags(lock, 0)
#define __raw_spin_unlock_wait(x) \ #define __raw_spin_unlock_wait(x) \
do { cpu_relax(); } while (__raw_spin_is_locked(x)) do { cpu_relax(); } while (__raw_spin_is_locked(x))
static inline void __raw_spin_lock(raw_spinlock_t *x) static inline void __raw_spin_lock_flags(raw_spinlock_t *x,
unsigned long flags)
{ {
volatile unsigned int *a; volatile unsigned int *a;
mb(); mb();
a = __ldcw_align(x); a = __ldcw_align(x);
while (__ldcw(a) == 0) while (__ldcw(a) == 0)
while (*a == 0); while (*a == 0)
if (flags & PSW_SM_I) {
local_irq_enable();
cpu_relax();
local_irq_disable();
} else
cpu_relax();
mb(); mb();
} }
@ -60,26 +67,20 @@ static inline int __raw_spin_trylock(raw_spinlock_t *x)
static __inline__ void __raw_read_lock(raw_rwlock_t *rw) static __inline__ void __raw_read_lock(raw_rwlock_t *rw)
{ {
unsigned long flags;
local_irq_save(flags);
__raw_spin_lock(&rw->lock); __raw_spin_lock(&rw->lock);
rw->counter++; rw->counter++;
__raw_spin_unlock(&rw->lock); __raw_spin_unlock(&rw->lock);
local_irq_restore(flags);
} }
static __inline__ void __raw_read_unlock(raw_rwlock_t *rw) static __inline__ void __raw_read_unlock(raw_rwlock_t *rw)
{ {
unsigned long flags;
local_irq_save(flags);
__raw_spin_lock(&rw->lock); __raw_spin_lock(&rw->lock);
rw->counter--; rw->counter--;
__raw_spin_unlock(&rw->lock); __raw_spin_unlock(&rw->lock);
local_irq_restore(flags);
} }
/* write_lock is less trivial. We optimistically grab the lock and check /* write_lock is less trivial. We optimistically grab the lock and check