Messages in this thread Patch in this message | | | Date | Thu, 2 Jul 2015 01:03:11 +0200 | From | Oleg Nesterov <> | Subject | [PATCH v2 4/5] mremap: don't do uneccesary checks if new_len == old_len |
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The "new_len > old_len" branch in vma_to_resize() looks very confusing. It only covers the VM_DONTEXPAND/pgoff checks but everything below is equally unneeded if new_len == old_len.
Change this code to return if "new_len == old_len", new_len < old_len is not possible, otherwise the code below is wrong anyway.
Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: David Rientjes <rientjes@google.com> --- mm/mremap.c | 21 +++++++++++---------- 1 files changed, 11 insertions(+), 10 deletions(-)
diff --git a/mm/mremap.c b/mm/mremap.c index 7dcf7b4..d3f42be 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -346,6 +346,7 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr, { struct mm_struct *mm = current->mm; struct vm_area_struct *vma = find_vma(mm, addr); + unsigned long pgoff; if (!vma || vma->vm_start > addr) return ERR_PTR(-EFAULT); @@ -357,17 +358,17 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr, if (old_len > vma->vm_end - addr) return ERR_PTR(-EFAULT); + if (new_len == old_len) + return vma; + /* Need to be careful about a growing mapping */ - if (new_len > old_len) { - unsigned long pgoff; - - if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)) - return ERR_PTR(-EFAULT); - pgoff = (addr - vma->vm_start) >> PAGE_SHIFT; - pgoff += vma->vm_pgoff; - if (pgoff + (new_len >> PAGE_SHIFT) < pgoff) - return ERR_PTR(-EINVAL); - } + pgoff = (addr - vma->vm_start) >> PAGE_SHIFT; + pgoff += vma->vm_pgoff; + if (pgoff + (new_len >> PAGE_SHIFT) < pgoff) + return ERR_PTR(-EINVAL); + + if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)) + return ERR_PTR(-EFAULT); if (vma->vm_flags & VM_LOCKED) { unsigned long locked, lock_limit; -- 1.5.5.1
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