Messages in this thread | | | Date | Sun, 16 Oct 2005 10:04:21 +1000 | From | Nick Piggin <> | Subject | Re: Possible memory ordering bug in page reclaim? |
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Linus Torvalds wrote:
> I agree, however, that it looks like PG_dirty is racy. Probably not in > practice, but still. > > So I'd suggest adding a smp_wmb() into set_page_dirty, and the rmb where > Nick suggested. > > So I'd suggest a patch something more like this.. Marking the dirty/count > cases unlikely too in mm/page-writeback.c, since we should have tested for > these conditions optimistically outside the lock. >
As Dave suggested, I think there is too much other code that depends on these atomics to be barriers for us to change it (at least not in this patch! :)).
> Comments? Nick, did you have some test-case that you think might actually > have been impacted by this? >
I guess your vmscan.c hunks are slightly nicer, though I might put 'cannot_free' right at the end, because it will be a very uncommon case.
And no, I don't have a test case. In fact, I wouldn't be surprised if nobody anywhere has ever hit it :) I was just browsing code...
Thanks, Nick
-- SUSE Labs, Novell Inc.
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