From: Andi Kleen Date: Wed, 6 Aug 2014 23:06:49 +0000 (-0700) Subject: hwpoison: fix race with changing page during offlining X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=f37d4298aa7f8b74395aa13c728677e2ed86fdaf;p=linux-beck.git hwpoison: fix race with changing page during offlining When a hwpoison page is locked it could change state due to parallel modifications. The original compound page can be torn down and then this 4k page becomes part of a differently-size compound page is is a standalone regular page. Check after the lock if the page is still the same compound page. We could go back, grab the new head page and try again but it should be quite rare, so I thought this was safest. A retry loop would be more difficult to test and may have more side effects. The hwpoison code by design only tries to handle cases that are reasonably common in workloads, as visible in page-flags. I'm not really that concerned about handling this (likely rare case), just not crashing on it. Signed-off-by: Andi Kleen Acked-by: Naoya Horiguchi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/memory-failure.c b/mm/memory-failure.c index a013bc94ebbe..44c6bd201d3a 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -1172,6 +1172,16 @@ int memory_failure(unsigned long pfn, int trapno, int flags) lock_page(hpage); + /* + * The page could have changed compound pages during the locking. + * If this happens just bail out. + */ + if (compound_head(p) != hpage) { + action_result(pfn, "different compound page after locking", IGNORED); + res = -EBUSY; + goto out; + } + /* * We use page flags to determine what action should be taken, but * the flags can be modified by the error containment action. One