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32b154c0b0
Addresses http://bugzilla.kernel.org/show_bug.cgi?id=13302 On x86 and x86-64, it is possible that page tables are shared beween shared mappings backed by hugetlbfs. As part of this, page_table_shareable() checks a pair of vma->vm_flags and they must match if they are to be shared. All VMA flags are taken into account, including VM_LOCKED. The problem is that VM_LOCKED is cleared on fork(). When a process with a shared memory segment forks() to exec() a helper, there will be shared VMAs with different flags. The impact is that the shared segment is sometimes considered shareable and other times not, depending on what process is checking. What happens is that the segment page tables are being shared but the count is inaccurate depending on the ordering of events. As the page tables are freed with put_page(), bad pmd's are found when some of the children exit. The hugepage counters also get corrupted and the Total and Free count will no longer match even when all the hugepage-backed regions are freed. This requires a reboot of the machine to "fix". This patch addresses the problem by comparing all flags except VM_LOCKED when deciding if pagetables should be shared or not for hugetlbfs-backed mapping. Signed-off-by: Mel Gorman <mel@csn.ul.ie> Acked-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Cc: Ingo Molnar <mingo@elte.hu> Cc: <stable@kernel.org> Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: <starlight@binnacle.cx> Cc: Eric B Munson <ebmunson@us.ibm.com> Cc: Adam Litke <agl@us.ibm.com> Cc: Andy Whitcroft <apw@canonical.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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