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SubjectRe: [PATCH 6/8] i386: bitops: Don't mark memory as clobbered unnecessarily
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On Tue, 2007-07-24 at 11:13 -0700, Linus Torvalds wrote:
>
> 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.

Yup, and this is exactly what we currently do in bit_spin_unlock().

Trond

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