Messages in this thread | | | Date | Wed, 18 May 2016 10:21:01 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH v1] mm: bad_page() checks bad_flags instead of page->flags for hwpoison page |
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On Tue, May 17, 2016 at 04:42:55PM +0900, Naoya Horiguchi wrote: > There's a race window between checking page->flags and unpoisoning, which > taints kernel with "BUG: Bad page state". That's overkill. It's safer to > use bad_flags to detect hwpoisoned page. >
I'm not quite getting this one. Minimally, instead of = __PG_HWPOISON, it should have been (bad_flags & __PG_POISON). As Vlastimil already pointed out, __PG_HWPOISON can be 0. What I'm not getting is why this fixes the race. The current race is
1. Check poison, set bad_flags 2. poison clears in parallel 3. Check page->flag state in bad_page and trigger warning
The code changes it to
1. Check poison, set bad_flags 2. poison clears in parallel 3. Check bad_flags and trigger warning
There is warning either way. What did I miss?
-- Mel Gorman SUSE Labs
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