08dc2ca61e
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>
148 lines
3.1 KiB
C
148 lines
3.1 KiB
C
#ifndef __ASM_SPINLOCK_H
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#define __ASM_SPINLOCK_H
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#include <asm/system.h>
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#include <asm/processor.h>
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#include <asm/spinlock_types.h>
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static inline int __raw_spin_is_locked(raw_spinlock_t *x)
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{
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volatile unsigned int *a = __ldcw_align(x);
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return *a == 0;
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}
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#define __raw_spin_lock(lock) __raw_spin_lock_flags(lock, 0)
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#define __raw_spin_unlock_wait(x) \
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do { cpu_relax(); } while (__raw_spin_is_locked(x))
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static inline void __raw_spin_lock_flags(raw_spinlock_t *x,
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unsigned long flags)
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{
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volatile unsigned int *a;
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mb();
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a = __ldcw_align(x);
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while (__ldcw(a) == 0)
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while (*a == 0)
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if (flags & PSW_SM_I) {
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local_irq_enable();
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cpu_relax();
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local_irq_disable();
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} else
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cpu_relax();
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mb();
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}
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static inline void __raw_spin_unlock(raw_spinlock_t *x)
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{
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volatile unsigned int *a;
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mb();
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a = __ldcw_align(x);
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*a = 1;
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mb();
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}
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static inline int __raw_spin_trylock(raw_spinlock_t *x)
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{
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volatile unsigned int *a;
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int ret;
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mb();
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a = __ldcw_align(x);
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ret = __ldcw(a) != 0;
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mb();
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return ret;
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}
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/*
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* Read-write spinlocks, allowing multiple readers
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* but only one writer.
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*/
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#define __raw_read_trylock(lock) generic__raw_read_trylock(lock)
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/* read_lock, read_unlock are pretty straightforward. Of course it somehow
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* sucks we end up saving/restoring flags twice for read_lock_irqsave aso. */
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static __inline__ void __raw_read_lock(raw_rwlock_t *rw)
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{
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__raw_spin_lock(&rw->lock);
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rw->counter++;
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__raw_spin_unlock(&rw->lock);
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}
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static __inline__ void __raw_read_unlock(raw_rwlock_t *rw)
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{
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__raw_spin_lock(&rw->lock);
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rw->counter--;
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__raw_spin_unlock(&rw->lock);
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}
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/* write_lock is less trivial. We optimistically grab the lock and check
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* if we surprised any readers. If so we release the lock and wait till
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* they're all gone before trying again
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*
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* Also note that we don't use the _irqsave / _irqrestore suffixes here.
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* If we're called with interrupts enabled and we've got readers (or other
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* writers) in interrupt handlers someone fucked up and we'd dead-lock
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* sooner or later anyway. prumpf */
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static __inline__ void __raw_write_lock(raw_rwlock_t *rw)
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{
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retry:
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__raw_spin_lock(&rw->lock);
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if(rw->counter != 0) {
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/* this basically never happens */
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__raw_spin_unlock(&rw->lock);
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while (rw->counter != 0)
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cpu_relax();
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goto retry;
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}
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/* got it. now leave without unlocking */
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rw->counter = -1; /* remember we are locked */
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}
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/* write_unlock is absolutely trivial - we don't have to wait for anything */
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static __inline__ void __raw_write_unlock(raw_rwlock_t *rw)
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{
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rw->counter = 0;
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__raw_spin_unlock(&rw->lock);
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}
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static __inline__ int __raw_write_trylock(raw_rwlock_t *rw)
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{
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__raw_spin_lock(&rw->lock);
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if (rw->counter != 0) {
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/* this basically never happens */
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__raw_spin_unlock(&rw->lock);
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return 0;
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}
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/* got it. now leave without unlocking */
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rw->counter = -1; /* remember we are locked */
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return 1;
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}
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static __inline__ int __raw_is_read_locked(raw_rwlock_t *rw)
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{
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return rw->counter > 0;
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}
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static __inline__ int __raw_is_write_locked(raw_rwlock_t *rw)
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{
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return rw->counter < 0;
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}
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#endif /* __ASM_SPINLOCK_H */
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