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author | Hugh Dickins <hughd@google.com> | 2012-11-16 14:15:03 -0800 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-11-16 14:33:04 -0800 |
commit | 215c02bc33bbd5ff4d7379a909462d11f0103218 (patch) | |
tree | fa07d774e4b60404727ca0a8d54044d439eef905 | |
parent | 498c2280212327858e521e9d21345d4cc2637f54 (diff) | |
download | linux-3.10-215c02bc33bbd5ff4d7379a909462d11f0103218.tar.gz linux-3.10-215c02bc33bbd5ff4d7379a909462d11f0103218.tar.bz2 linux-3.10-215c02bc33bbd5ff4d7379a909462d11f0103218.zip |
tmpfs: fix shmem_getpage_gfp() VM_BUG_ON
Fuzzing with trinity hit the "impossible" VM_BUG_ON(error) (which Fedora
has converted to WARNING) in shmem_getpage_gfp():
WARNING: at mm/shmem.c:1151 shmem_getpage_gfp+0xa5c/0xa70()
Pid: 29795, comm: trinity-child4 Not tainted 3.7.0-rc2+ #49
Call Trace:
warn_slowpath_common+0x7f/0xc0
warn_slowpath_null+0x1a/0x20
shmem_getpage_gfp+0xa5c/0xa70
shmem_fault+0x4f/0xa0
__do_fault+0x71/0x5c0
handle_pte_fault+0x97/0xae0
handle_mm_fault+0x289/0x350
__do_page_fault+0x18e/0x530
do_page_fault+0x2b/0x50
page_fault+0x28/0x30
tracesys+0xe1/0xe6
Thanks to Johannes for pointing to truncation: free_swap_and_cache()
only does a trylock on the page, so the page lock we've held since
before confirming swap is not enough to protect against truncation.
What cleanup is needed in this case? Just delete_from_swap_cache(),
which takes care of the memcg uncharge.
Signed-off-by: Hugh Dickins <hughd@google.com>
Reported-by: Dave Jones <davej@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | mm/shmem.c | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/mm/shmem.c b/mm/shmem.c index 67afba5117f..dc12264f44f 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1145,8 +1145,20 @@ repeat: if (!error) { error = shmem_add_to_page_cache(page, mapping, index, gfp, swp_to_radix_entry(swap)); - /* We already confirmed swap, and make no allocation */ - VM_BUG_ON(error); + /* + * We already confirmed swap under page lock, and make + * no memory allocation here, so usually no possibility + * of error; but free_swap_and_cache() only trylocks a + * page, so it is just possible that the entry has been + * truncated or holepunched since swap was confirmed. + * shmem_undo_range() will have done some of the + * unaccounting, now delete_from_swap_cache() will do + * the rest (including mem_cgroup_uncharge_swapcache). + * Reset swap.val? No, leave it so "failed" goes back to + * "repeat": reading a hole and writing should succeed. + */ + if (error) + delete_from_swap_cache(page); } if (error) goto failed; |