3.5.7.2 -stable review patch. If anyone has any objections, please let me know.
------------------ From: Hugh Dickins <[email protected]> commit 215c02bc33bbd5ff4d7379a909462d11f0103218 upstream. 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 <[email protected]> Reported-by: Dave Jones <[email protected]> Cc: Johannes Weiner <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Herton Ronaldo Krzesinski <[email protected]> --- mm/shmem.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index 06d48ca..c7f7a77 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1154,8 +1154,20 @@ 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; -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
