Chen, Kenneth W wrote:
Nick Piggin wrote on Tuesday, March 28, 2006 12:11 AMOK, that's fair enough and I guess you do need a barrier there. However, should the mb__after barrier still remain? The comment in wake_up_bit suggests yes, and there is similar code in unlock_page.Question on unlock_page: void fastcall unlock_page(struct page *page) { smp_mb__before_clear_bit(); if (!TestClearPageLocked(page)) BUG(); smp_mb__after_clear_bit(); wake_up_page(page, PG_locked); } Assuming test_and_clear_bit() on all arch does what the API is called for with full memory fence around the atomic op, why do you need smp_mb__before_clear_bit and smp_mb__after_clear_bit? Aren't they redundant?
Yep. I pointed this out earlier. I'd say it may have initially just been a ClearPageLocked, and was changed for debugging reasons. We could instead change it to BUG_ON(!PageLocked(page); ClearPageLocked(page); /* this does clear_bit_for_unlock */ smp_mb__after_clear_bit_unlock(); wake_up_page --Send instant messages to your online friends http://au.messenger.yahoo.com -
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