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    Subject[PATCH v2 1/2] mm: fix incorrect behavior when process virtual address space limit is exceeded
    Date
    The following flag comparison in mmap_region makes no sense:

    if (!(vm_flags & MAP_FIXED))
    return -ENOMEM;

    The condition is false even if MAP_FIXED is not set what causes the
    unnecessary find_vma call. MAP_FIXED has the same value as VM_MAYREAD.
    The vm_flags must not be compared with MAP_FIXED. The vm_flags may only
    be compared with VM_* flags. The mmap executes slightly longer when
    MAP_FIXED is not set and RLIMIT_AS is exceeded.

    Fix the issue by introducing a new parameter to mmap_region which forwards
    the mmap flags and now the MAP_FIXED can be checked properly.
    Tile and its arch_setup_additional_pages as the user of
    mmap_region has to be specific about its mmap flags now.

    Signed-off-by: Piotr Kwapulinski <kwapulinski.piotr@gmail.com>
    ---
    arch/tile/mm/elf.c | 1 +
    include/linux/mm.h | 3 ++-
    mm/mmap.c | 7 ++++---
    3 files changed, 7 insertions(+), 4 deletions(-)

    diff --git a/arch/tile/mm/elf.c b/arch/tile/mm/elf.c
    index 6225cc9..dae4b33 100644
    --- a/arch/tile/mm/elf.c
    +++ b/arch/tile/mm/elf.c
    @@ -142,6 +142,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
    if (!retval) {
    unsigned long addr = MEM_USER_INTRPT;
    addr = mmap_region(NULL, addr, INTRPT_SIZE,
    + MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE,
    VM_READ|VM_EXEC|
    VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC, 0);
    if (addr > (unsigned long) -PAGE_SIZE)
    diff --git a/include/linux/mm.h b/include/linux/mm.h
    index 00bad77..f1a203f 100644
    --- a/include/linux/mm.h
    +++ b/include/linux/mm.h
    @@ -1911,7 +1911,8 @@ extern int install_special_mapping(struct mm_struct *mm,
    extern unsigned long get_unmapped_area(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);

    extern unsigned long mmap_region(struct file *file, unsigned long addr,
    - unsigned long len, vm_flags_t vm_flags, unsigned long pgoff);
    + unsigned long len, unsigned long mmap_flags,
    + vm_flags_t vm_flags, unsigned long pgoff);
    extern unsigned long do_mmap(struct file *file, unsigned long addr,
    unsigned long len, unsigned long prot, unsigned long flags,
    vm_flags_t vm_flags, unsigned long pgoff, unsigned long *populate);
    diff --git a/mm/mmap.c b/mm/mmap.c
    index 2ce04a6..8f3427f 100644
    --- a/mm/mmap.c
    +++ b/mm/mmap.c
    @@ -1399,7 +1399,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
    vm_flags |= VM_NORESERVE;
    }

    - addr = mmap_region(file, addr, len, vm_flags, pgoff);
    + addr = mmap_region(file, addr, len, flags, vm_flags, pgoff);
    if (!IS_ERR_VALUE(addr) &&
    ((vm_flags & VM_LOCKED) ||
    (flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE))
    @@ -1535,7 +1535,8 @@ static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags)
    }

    unsigned long mmap_region(struct file *file, unsigned long addr,
    - unsigned long len, vm_flags_t vm_flags, unsigned long pgoff)
    + unsigned long len, unsigned long mmap_flags,
    + vm_flags_t vm_flags, unsigned long pgoff)
    {
    struct mm_struct *mm = current->mm;
    struct vm_area_struct *vma, *prev;
    @@ -1551,7 +1552,7 @@ 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))
    + if (!(mmap_flags & MAP_FIXED))
    return -ENOMEM;

    nr_pages = count_vma_pages_range(mm, addr, addr + len);
    --
    2.6.2


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