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authorWill Deacon <will.deacon@arm.com>2017-07-10 15:48:31 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-10 16:32:31 -0700
commitf4e177d12686bf98b5a047b5187121a71ee0dd8c (patch)
treed278c09e2bc610288c37b79747d727e489752597 /mm/memory_hotplug.c
parent108a7ac448caff8e35e8c3f92f65faad893e5aca (diff)
mm/migrate.c: stabilise page count when migrating transparent hugepages
When migrating a transparent hugepage, migrate_misplaced_transhuge_page guards itself against a concurrent fastgup of the page by checking that the page count is equal to 2 before and after installing the new pmd. If the page count changes, then the pmd is reverted back to the original entry, however there is a small window where the new (possibly writable) pmd is installed and the underlying page could be written by userspace. Restoring the old pmd could therefore result in loss of data. This patch fixes the problem by freezing the page count whilst updating the page tables, which protects against a concurrent fastgup without the need to restore the old pmd in the failure case (since the page count can no longer change under our feet). Link: http://lkml.kernel.org/r/1497349722-6731-4-git-send-email-will.deacon@arm.com Signed-off-by: Will Deacon <will.deacon@arm.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Steve Capper <steve.capper@arm.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memory_hotplug.c')
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