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    SubjectRe: [PATCH] mm/mmap.c: remove incorrect MAP_FIXED flag comparison from mmap_region
    On Tue, 17 Nov 2015 18:26:38 +0100 Piotr Kwapulinski <kwapulinski.piotr@gmail.com> wrote:

    > The following flag comparison in mmap_region is not fully correct:
    >
    > if (!(vm_flags & MAP_FIXED))
    >
    > The vm_flags should not be compared with MAP_FIXED (0x10). It is a bit
    > confusing. This condition is almost always true since VM_MAYREAD (0x10)
    > flag is almost always set by default. This patch removes this condition.
    >
    > ...
    >
    > --- a/mm/mmap.c
    > +++ b/mm/mmap.c
    > @@ -1547,13 +1547,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
    > if (!may_expand_vm(mm, len >> PAGE_SHIFT)) {
    > unsigned long nr_pages;
    >
    > - /*
    > - * MAP_FIXED may remove pages of mappings that intersects with
    > - * requested mapping. Account for the pages it would unmap.
    > - */
    > - if (!(vm_flags & MAP_FIXED))
    > - return -ENOMEM;
    > -
    > nr_pages = count_vma_pages_range(mm, addr, addr + len);
    >
    > if (!may_expand_vm(mm, (len >> PAGE_SHIFT) - nr_pages))

    That looks simpler.

    However the changelog doesn't describe the end-user visible effects of
    the bug, as changelogs should always do. Presumably this is causing
    incorrect ENOMEM reporting due to RLIMIT_AS being exceeded, but this
    isn't very specific.

    So can you please fill in the details here? Such info is needed when
    deciding which kernel version(s) need the fix.

    Thanks.


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