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    SubjectRe: [PATCH v3] mm/mmap.c: remove incorrect MAP_FIXED flag comparison from mmap_region
    On Mon, 23 Nov 2015 18:36:42 +0100 Piotr Kwapulinski <kwapulinski.piotr@gmail.com> wrote:

    > The following flag comparison in mmap_region makes no sense:
    >
    > if (!(vm_flags & MAP_FIXED))
    > return -ENOMEM;
    >
    > The condition is always false and thus the above "return -ENOMEM" is never
    > executed. The vm_flags must not be compared with MAP_FIXED flag.
    > The vm_flags may only be compared with VM_* flags.
    > MAP_FIXED has the same value as VM_MAYREAD.
    > Hitting the rlimit is a slow path and find_vma_intersection should realize
    > that there is no overlapping VMA for !MAP_FIXED case pretty quickly.
    >
    > Remove the code that makes no sense.
    >
    > ...
    >
    > --- a/mm/mmap.c
    > +++ b/mm/mmap.c
    > @@ -1551,9 +1551,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
    > * 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))

    Did you intend to retain the stale comment?


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