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    SubjectRe: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM_LOCKED file segments
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    On Thu, Jan 29, 2009 at 12:48 PM, Linus Torvalds
    <torvalds@linux-foundation.org> wrote:
    >
    > On Thu, 29 Jan 2009, Linus Torvalds wrote:
    >>
    >> THIS PATCH IS TOTALLY UNTESTED!
    >
    > Well, it boots. FWIW. I've not really tested anything interesting with it,
    > but any potential breakage is at least not catastrophic and immediate.
    >
    >> diff --git a/mm/mmap.c b/mm/mmap.c
    >> index 8d95902..3f78ead 100644
    >> --- a/mm/mmap.c
    >> +++ b/mm/mmap.c
    >> @@ -769,6 +769,10 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
    >> if (vm_flags & VM_SPECIAL)
    >> return NULL;
    >>
    >> + /* Anonymous shared mappings are unsharable */
    >> + if ((vm_flags & VM_SHARED) && !file)
    >> + return NULL;
    >> +
    >
    > .. and I think this part of it is actually unnecessary, because what
    > happens is that a shared anon mapping is turned into a shmem mapping when
    > it is inserted, and that actually ends up allocating a file for it. So the
    > vma->vm_file for anon mappings will not match a NULL file pointer
    > _anyway_, so there's no way it would end up merging.
    >
    > So my patch can be further simplified, I think, to just the following.
    > Even more total lines removed.
    >
    > I still want somebody else to look at and think about it, though.

    Just to confirm. This patch also appear to fix the immediate issue for us.

    thanks,
    max


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