s390/rwlock: improve writer fairness (94232a43) · Commits · 戴 / test

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>

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);

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