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mm/fremap.c: fix possible oops on error path

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The vm_flags introduced in 6d7825b10d ("mm/fremap.c: fix oops on error
path") is supposed to avoid a compiler warning about unitialized
vm_flags without changing the generated code.

However I am concerned that this is going to be very brittle, and fail
with some compiler versions. The failure could be either of:

- compiler could actually load vma->vm_flags before checking for the
  !vma condition, thus reintroducing the oops

- compiler could optimize out the !vma check, since the pointer just got
  dereferenced shortly before (so the compiler knows it can't be NULL!)

I propose reversing this part of the change and initializing vm_flags to 0
just to avoid the bogus uninitialized use warning.

Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Tommi Rantala <tt.rantala@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michel Lespinasse 2013-03-14 16:50:02 -07:00 committed by Linus Torvalds
parent f4846e52c5
commit a2362d2476
1 changed files with 2 additions and 3 deletions
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5
mm/fremap.c
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@ -129,7 +129,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
struct vm_area_struct *vma;
int err = -EINVAL;
int has_write_lock = 0;
vm_flags_t vm_flags;
vm_flags_t vm_flags = 0;
if (prot)
return err;
@ -163,8 +163,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
* and that the remapped range is valid and fully within
* the single existing vma.
*/
vm_flags = vma->vm_flags;
if (!vma || !(vm_flags & VM_SHARED))
if (!vma || !(vma->vm_flags & VM_SHARED))
goto out;
if (!vma->vm_ops || !vma->vm_ops->remap_pages)