Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobberedunnecessarily

[Linus Torvalds]

On Tue, 24 Jul 2007, Trond Myklebust wrote:
> 
> That's not what the Documentation/memory-barriers.txt states:

Hmm.. You're right. We only actually need it for the unconditional bitops, 
like the *unlock* side.

IOW, if you do a spinlock with the bitops, the locking side should be able 
to use a "test_and_set_bit()" on its own, but the unlocking side should be

	smp_mb__before_clear_bit();
	clear_bit();

because the ones that don't return a value also don't imply a memory 
barrier.

		Linus
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