diff options
| author | Leon Yu <chianglungyu@gmail.com> | 2015-03-26 01:55:11 +0300 |
|---|---|---|
| committer | Luis Henriques <luis.henriques@canonical.com> | 2015-04-10 12:04:05 +0300 |
| commit | 2ac1a1089a0d040999da34c93d1d8135db2bf67e (patch) | |
| tree | 0e80989f84842f99e8219367ade67f35d8f5722d /mm/rmap.c | |
| parent | d4af55bd8e4f9151aecbeace0446aa8d272841c9 (diff) | |
| download | linux-2ac1a1089a0d040999da34c93d1d8135db2bf67e.tar.xz | |
mm: fix anon_vma->degree underflow in anon_vma endless growing prevention
commit 3fe89b3e2a7bbf3e97657104b9b33a9d81b950b3 upstream.
I have constantly stumbled upon "kernel BUG at mm/rmap.c:399!" after
upgrading to 3.19 and had no luck with 4.0-rc1 neither.
So, after looking into new logic introduced by commit 7a3ef208e662 ("mm:
prevent endless growth of anon_vma hierarchy"), I found chances are that
unlink_anon_vmas() is called without incrementing dst->anon_vma->degree
in anon_vma_clone() due to allocation failure. If dst->anon_vma is not
NULL in error path, its degree will be incorrectly decremented in
unlink_anon_vmas() and eventually underflow when exiting as a result of
another call to unlink_anon_vmas(). That's how "kernel BUG at
mm/rmap.c:399!" is triggered for me.
This patch fixes the underflow by dropping dst->anon_vma when allocation
fails. It's safe to do so regardless of original value of dst->anon_vma
because dst->anon_vma doesn't have valid meaning if anon_vma_clone()
fails. Besides, callers don't care dst->anon_vma in such case neither.
Also suggested by Michal Hocko, we can clean up vma_adjust() a bit as
anon_vma_clone() now does the work.
[akpm@linux-foundation.org: tweak comment]
Fixes: 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy")
Signed-off-by: Leon Yu <chianglungyu@gmail.com>
Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
Diffstat (limited to 'mm/rmap.c')
| -rw-r--r-- | mm/rmap.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/mm/rmap.c b/mm/rmap.c index ab8e7984fa19..e84beb4dcfce 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -287,6 +287,13 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src) return 0; enomem_failure: + /* + * dst->anon_vma is dropped here otherwise its degree can be incorrectly + * decremented in unlink_anon_vmas(). + * We can safely do this because callers of anon_vma_clone() don't care + * about dst->anon_vma if anon_vma_clone() failed. + */ + dst->anon_vma = NULL; unlink_anon_vmas(dst); return -ENOMEM; } |