Messages in this thread | | | Date | Mon, 27 Mar 2006 20:56:46 +1000 | From | Nick Piggin <> | Subject | Re: unlock_buffer() and clear_bit() |
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Nick Piggin wrote:
> smp_mb__after_clear_bit() is supposed to, when run directly after > a clear_bit operation, provide the equivalent of an smp_mb(). >
Actually I guess I'm wrong here: it appears that it really should order before, and after the clear_bit, respectively (looking at its usage in unlock_page.
So ia64's smp_mb__before_clear_bit needs to be a full barrier, but __after_clear_bit can be a release. I think?
By the way unlock_page is issuing extra barriers: Documentation/atomic_ops.txt defines test_and_clear_bit operations to provide full memory barriers before and after them, so no need for smp_mb__before/after there.
...ia64 gets these test_and_x_bit operations wrong as well...
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