From patchwork Fri Dec 7 16:06:09 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [3.5.y.z, extended, stable] Patch "tmpfs: fix shmem_getpage_gfp() VM_BUG_ON" has been added to staging queue Date: Fri, 07 Dec 2012 06:06:09 -0000 From: Herton Ronaldo Krzesinski X-Patchwork-Id: 204565 Message-Id: <1354896369-23175-1-git-send-email-herton.krzesinski@canonical.com> To: Hugh Dickins Cc: kernel-team@lists.ubuntu.com, Johannes Weiner , Dave Jones , Andrew Morton , Linus Torvalds This is a note to let you know that I have just added a patch titled tmpfs: fix shmem_getpage_gfp() VM_BUG_ON to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.5.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Herton ------ >From ccb8539a11acffd2012be03ac3dc70ae4597bf62 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Fri, 16 Nov 2012 14:15:03 -0800 Subject: [PATCH] tmpfs: fix shmem_getpage_gfp() VM_BUG_ON 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 Reported-by: Dave Jones Cc: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Herton Ronaldo Krzesinski --- mm/shmem.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) -- 1.7.9.5 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;