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authorLiu Bo <bo.li.liu@oracle.com>2013-10-01 23:49:49 +0800
committerJosef Bacik <jbacik@fusionio.com>2013-10-04 16:02:11 -0400
commit385fe0bede52a45cd960f30c7eb8d20ad8e1e05b (patch)
tree751e4561ac6c656bb70502ec87a574181b64b641 /fs
parent60e7cd3a4ba6049ef590921e84454e6cfd9e2589 (diff)
downloadlinux-385fe0bede52a45cd960f30c7eb8d20ad8e1e05b.tar.gz
Btrfs: fix crash of compressed writes
The crash[1] is found by xfstests/generic/208 with "-o compress", it's not reproduced everytime, but it does panic. The bug is quite interesting, it's actually introduced by a recent commit (573aecafca1cf7a974231b759197a1aebcf39c2a, Btrfs: actually limit the size of delalloc range). Btrfs implements delay allocation, so during writeback, we (1) get a page A and lock it (2) search the state tree for delalloc bytes and lock all pages within the range (3) process the delalloc range, including find disk space and create ordered extent and so on. (4) submit the page A. It runs well in normal cases, but if we're in a racy case, eg. buffered compressed writes and aio-dio writes, sometimes we may fail to lock all pages in the 'delalloc' range, in which case, we need to fall back to search the state tree again with a smaller range limit(max_bytes = PAGE_CACHE_SIZE - offset). The mentioned commit has a side effect, that is, in the fallback case, we can find delalloc bytes before the index of the page we already have locked, so we're in the case of (delalloc_end <= *start) and return with (found > 0). This ends with not locking delalloc pages but making ->writepage still process them, and the crash happens. This fixes it by just thinking that we find nothing and returning to caller as the caller knows how to deal with it properly. [1]: ------------[ cut here ]------------ kernel BUG at mm/page-writeback.c:2170! [...] CPU: 2 PID: 11755 Comm: btrfs-delalloc- Tainted: G O 3.11.0+ #8 [...] RIP: 0010:[<ffffffff810f5093>] [<ffffffff810f5093>] clear_page_dirty_for_io+0x1e/0x83 [...] [ 4934.248731] Stack: [ 4934.248731] ffff8801477e5dc8 ffffea00049b9f00 ffff8801869f9ce8 ffffffffa02b841a [ 4934.248731] 0000000000000000 0000000000000000 0000000000000fff 0000000000000620 [ 4934.248731] ffff88018db59c78 ffffea0005da8d40 ffffffffa02ff860 00000001810016c0 [ 4934.248731] Call Trace: [ 4934.248731] [<ffffffffa02b841a>] extent_range_clear_dirty_for_io+0xcf/0xf5 [btrfs] [ 4934.248731] [<ffffffffa02a8889>] compress_file_range+0x1dc/0x4cb [btrfs] [ 4934.248731] [<ffffffff8104f7af>] ? detach_if_pending+0x22/0x4b [ 4934.248731] [<ffffffffa02a8bad>] async_cow_start+0x35/0x53 [btrfs] [ 4934.248731] [<ffffffffa02c694b>] worker_loop+0x14b/0x48c [btrfs] [ 4934.248731] [<ffffffffa02c6800>] ? btrfs_queue_worker+0x25c/0x25c [btrfs] [ 4934.248731] [<ffffffff810608f5>] kthread+0x8d/0x95 [ 4934.248731] [<ffffffff81060868>] ? kthread_freezable_should_stop+0x43/0x43 [ 4934.248731] [<ffffffff814fe09c>] ret_from_fork+0x7c/0xb0 [ 4934.248731] [<ffffffff81060868>] ? kthread_freezable_should_stop+0x43/0x43 [ 4934.248731] Code: ff 85 c0 0f 94 c0 0f b6 c0 59 5b 5d c3 0f 1f 44 00 00 55 48 89 e5 41 54 53 48 89 fb e8 2c de 00 00 49 89 c4 48 8b 03 a8 01 75 02 <0f> 0b 4d 85 e4 74 52 49 8b 84 24 80 00 00 00 f6 40 20 01 75 44 [ 4934.248731] RIP [<ffffffff810f5093>] clear_page_dirty_for_io+0x1e/0x83 [ 4934.248731] RSP <ffff8801869f9c48> [ 4934.280307] ---[ end trace 36f06d3f8750236a ]--- Signed-off-by: Liu Bo <bo.li.liu@oracle.com> Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Diffstat (limited to 'fs')
-rw-r--r--fs/btrfs/extent_io.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index c09a40db53d..43feb4663f5 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1614,7 +1614,7 @@ again:
*start = delalloc_start;
*end = delalloc_end;
free_extent_state(cached_state);
- return found;
+ return 0;
}
/*