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    Subject[PATCH 3.2 002/153] mm/madvise.c: fix madvise() infinite loop under special circumstances
    3.2.102-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: chenjie <chenjie6@huawei.com>

    commit 6ea8d958a2c95a1d514015d4e29ba21a8c0a1a91 upstream.

    MADVISE_WILLNEED has always been a noop for DAX (formerly XIP) mappings.
    Unfortunately madvise_willneed() doesn't communicate this information
    properly to the generic madvise syscall implementation. The calling
    convention is quite subtle there. madvise_vma() is supposed to either
    return an error or update &prev otherwise the main loop will never
    advance to the next vma and it will keep looping for ever without a way
    to get out of the kernel.

    It seems this has been broken since introduction. Nobody has noticed
    because nobody seems to be using MADVISE_WILLNEED on these DAX mappings.

    [mhocko@suse.com: rewrite changelog]
    Link: http://lkml.kernel.org/r/20171127115318.911-1-guoxuenan@huawei.com
    Fixes: fe77ba6f4f97 ("[PATCH] xip: madvice/fadvice: execute in place")
    Signed-off-by: chenjie <chenjie6@huawei.com>
    Signed-off-by: guoxuenan <guoxuenan@huawei.com>
    Acked-by: Michal Hocko <mhocko@suse.com>
    Cc: Minchan Kim <minchan@kernel.org>
    Cc: zhangyi (F) <yi.zhang@huawei.com>
    Cc: Miao Xie <miaoxie@huawei.com>
    Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
    Cc: Shaohua Li <shli@fb.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Mel Gorman <mgorman@techsingularity.net>
    Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Carsten Otte <cotte@de.ibm.com>
    Cc: Dan Williams <dan.j.williams@intel.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    [bwh: Backported to 3.2: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    --- a/mm/madvise.c
    +++ b/mm/madvise.c
    @@ -128,6 +128,7 @@ static long madvise_willneed(struct vm_a
    {
    struct file *file = vma->vm_file;

    + *prev = vma;
    if (!file)
    return -EBADF;

    @@ -136,7 +137,6 @@ static long madvise_willneed(struct vm_a
    return 0;
    }

    - *prev = vma;
    start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
    if (end > vma->vm_end)
    end = vma->vm_end;
    \
     
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