Messages in this thread | | | Date | Fri, 2 Dec 2016 09:49:33 +0000 | From | Mel Gorman <> | Subject | Re: [PATCH 1/2] mm, page_alloc: Keep pcp count and list contents in sync if struct page is corrupted |
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On Fri, Dec 02, 2016 at 09:12:17AM +0100, Michal Hocko wrote: > On Fri 02-12-16 00:22:43, Mel Gorman wrote: > > Vlastimil Babka pointed out that commit 479f854a207c ("mm, page_alloc: > > defer debugging checks of pages allocated from the PCP") will allow the > > per-cpu list counter to be out of sync with the per-cpu list contents > > if a struct page is corrupted. This patch keeps the accounting in sync. > > > > Fixes: 479f854a207c ("mm, page_alloc: defer debugging checks of pages allocated from the PCP") > > Signed-off-by: Mel Gorman <mgorman@suse.de> > > cc: stable@vger.kernel.org [4.7+] > > I am trying to think about what would happen if we did go out of sync > and cannot spot a problem. Vlastimil has mentioned something about > free_pcppages_bulk looping for ever but I cannot see it happening right > now.
free_pcppages_bulk can infinite loop if the page count is positive and there are no pages. While I've only seen this during development, a corrupted count loops here
do { batch_free++; if (++pindex == NR_PCP_LISTS) pindex = 0; list = &pcp->lists[pindex]; } while (list_empty(list));
It would only be seen in a situation where struct page corruption was detected so it's rare.
-- Mel Gorman SUSE Labs
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