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mm: page_mkclean vs MADV_DONTNEED race
MADV_DONTNEED is handled with mmap_sem taken in read mode. We call page_mkclean without holding mmap_sem. MADV_DONTNEED implies that pages in the region are unmapped and subsequent access to the pages in that range is handled as a new page fault. This implies that if we don't have parallel access to the region when MADV_DONTNEED is run we expect those range to be unallocated. w.r.t page_mkclean() we need to make sure that we don't break the MADV_DONTNEED semantics. MADV_DONTNEED check for pmd_none without holding pmd_lock. This implies we skip the pmd if we temporarily mark pmd none. Avoid doing that while marking the page clean. Keep the sequence same for dax too even though we don't support MADV_DONTNEED for dax mapping The bug was noticed by code review and I didn't observe any failures w.r.t test run. This is similar to commit 58ceeb6 Author: Kirill A. Shutemov <[email protected]> Date: Thu Apr 13 14:56:26 2017 -0700 thp: fix MADV_DONTNEED vs. MADV_FREE race commit ced1080 Author: Kirill A. Shutemov <[email protected]> Date: Thu Apr 13 14:56:20 2017 -0700 thp: fix MADV_DONTNEED vs. numa balancing race Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Aneesh Kumar K.V <[email protected]> Reviewed-by: Andrew Morton <[email protected]> Cc: Dan Williams <[email protected]> Cc:"Kirill A . Shutemov" <[email protected]> Cc: Andrea Arcangeli <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
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