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s390/rwlock: improve writer fairness 

Set the write-lock bit in the out-of-line rwlock code to indicate that
a writer is waiting. Additional readers will no be able to get the lock
until at least one writer got the lock. Additional writers have to wait
for the first writer to release the lock again.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky 2014-09-22 16:25:25 +02:00
parent 2684e73a86
commit 94232a4332
1 changed files with 9 additions and 5 deletions
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14
arch/s390/lib/spinlock.c
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@ -149,9 +149,10 @@ EXPORT_SYMBOL(_raw_read_trylock_retry);
void _raw_write_lock_wait(arch_rwlock_t *rw)
{
unsigned int owner, old;
unsigned int owner, old, prev;
int count = spin_retry;
prev = 0x80000000;
owner = 0;
while (1) {
if (count-- <= 0) {
@ -161,10 +162,13 @@ void _raw_write_lock_wait(arch_rwlock_t *rw)
}
old = ACCESS_ONCE(rw->lock);
owner = ACCESS_ONCE(rw->owner);
if (old)
continue;
if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000))
return;
if ((int) old >= 0 &&
_raw_compare_and_swap(&rw->lock, old, old | 0x80000000))
prev = old;
else
smp_rmb();
if ((old & 0x7fffffff) == 0 && (int) prev >= 0)
break;
}
}
EXPORT_SYMBOL(_raw_write_lock_wait);