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Commit 94232a43 authored by Martin Schwidefsky's avatar Martin Schwidefsky
Browse files

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: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 2684e73a

arch/s390/lib/spinlock.c

+9 −5
Original line number Diff line number Diff line
@@ -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);