Btrfs: fix race between ranged fsync and writeback of adjacent ranges
commit 0c713cba upstream. When we do a full fsync (the bit BTRFS_INODE_NEEDS_FULL_SYNC is set in the inode) that happens to be ranged, which happens during a msync() or writes for files opened with O_SYNC for example, we can end up with a corrupt log, due to different file extent items representing ranges that overlap with each other, or hit some assertion failures. When doing a ranged fsync we only flush delalloc and wait for ordered exents within that range. If while we are logging items from our inode ordered extents for adjacent ranges complete, we end up in a race that can make us insert the file extent items that overlap with others we logged previously and the assertion failures. For example, if tree-log.c:copy_items() receives a leaf that has the following file extents items, all with a length of 4K and therefore there is an implicit hole in the range 68K to 72K - 1: (257 EXTENT_ITEM 64K), (257 EXTENT_ITEM 72K), (257 EXTENT_ITEM 76K), ... It copies them to the log tree. However due to the need to detect implicit holes, it may release the path, in order to look at the previous leaf to detect an implicit hole, and then later it will search again in the tree for the first file extent item key, with the goal of locking again the leaf (which might have changed due to concurrent changes to other inodes). However when it locks again the leaf containing the first key, the key corresponding to the extent at offset 72K may not be there anymore since there is an ordered extent for that range that is finishing (that is, somewhere in the middle of btrfs_finish_ordered_io()), and it just removed the file extent item but has not yet replaced it with a new file extent item, so the part of copy_items() that does hole detection will decide that there is a hole in the range starting from 68K to 76K - 1, and therefore insert a file extent item to represent that hole, having a key offset of 68K. After that we now have a log tree with 2 different extent items that have overlapping ranges: 1) The file extent item copied before copy_items() released the path, which has a key offset of 72K and a length of 4K, representing the file range 72K to 76K - 1. 2) And a file extent item representing a hole that has a key offset of 68K and a length of 8K, representing the range 68K to 76K - 1. This item was inserted after releasing the path, and overlaps with the extent item inserted before. The overlapping extent items can cause all sorts of unpredictable and incorrect behaviour, either when replayed or if a fast (non full) fsync happens later, which can trigger a BUG_ON() when calling btrfs_set_item_key_safe() through __btrfs_drop_extents(), producing a trace like the following: [61666.783269] ------------[ cut here ]------------ [61666.783943] kernel BUG at fs/btrfs/ctree.c:3182! [61666.784644] invalid opcode: 0000 [#1] PREEMPT SMP (...) [61666.786253] task: ffff880117b88c40 task.stack: ffffc90008168000 [61666.786253] RIP: 0010:btrfs_set_item_key_safe+0x7c/0xd2 [btrfs] [61666.786253] RSP: 0018:ffffc9000816b958 EFLAGS: 00010246 [61666.786253] RAX: 0000000000000000 RBX: 000000000000000f RCX: 0000000000030000 [61666.786253] RDX: 0000000000000000 RSI: ffffc9000816ba4f RDI: ffffc9000816b937 [61666.786253] RBP: ffffc9000816b998 R08: ffff88011dae2428 R09: 0000000000001000 [61666.786253] R10: 0000160000000000 R11: 6db6db6db6db6db7 R12: ffff88011dae2418 [61666.786253] R13: ffffc9000816ba4f R14: ffff8801e10c4118 R15: ffff8801e715c000 [61666.786253] FS: 00007f6060a18700(0000) GS:ffff88023f5c0000(0000) knlGS:0000000000000000 [61666.786253] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [61666.786253] CR2: 00007f6060a28000 CR3: 0000000213e69000 CR4: 00000000000006e0 [61666.786253] Call Trace: [61666.786253] __btrfs_drop_extents+0x5e3/0xaad [btrfs] [61666.786253] ? time_hardirqs_on+0x9/0x14 [61666.786253] btrfs_log_changed_extents+0x294/0x4e0 [btrfs] [61666.786253] ? release_extent_buffer+0x38/0xb4 [btrfs] [61666.786253] btrfs_log_inode+0xb6e/0xcdc [btrfs] [61666.786253] ? lock_acquire+0x131/0x1c5 [61666.786253] ? btrfs_log_inode_parent+0xee/0x659 [btrfs] [61666.786253] ? arch_local_irq_save+0x9/0xc [61666.786253] ? btrfs_log_inode_parent+0x1f5/0x659 [btrfs] [61666.786253] btrfs_log_inode_parent+0x223/0x659 [btrfs] [61666.786253] ? arch_local_irq_save+0x9/0xc [61666.786253] ? lockref_get_not_zero+0x2c/0x34 [61666.786253] ? rcu_read_unlock+0x3e/0x5d [61666.786253] btrfs_log_dentry_safe+0x60/0x7b [btrfs] [61666.786253] btrfs_sync_file+0x317/0x42c [btrfs] [61666.786253] vfs_fsync_range+0x8c/0x9e [61666.786253] SyS_msync+0x13c/0x1c9 [61666.786253] entry_SYSCALL_64_fastpath+0x18/0xad A sample of a corrupt log tree leaf with overlapping extents I got from running btrfs/072: item 14 key (295 108 200704) itemoff 2599 itemsize 53 extent data disk bytenr 0 nr 0 extent data offset 0 nr 458752 ram 458752 item 15 key (295 108 659456) itemoff 2546 itemsize 53 extent data disk bytenr 4343541760 nr 770048 extent data offset 606208 nr 163840 ram 770048 item 16 key (295 108 663552) itemoff 2493 itemsize 53 extent data disk bytenr 4343541760 nr 770048 extent data offset 610304 nr 155648 ram 770048 item 17 key (295 108 819200) itemoff 2440 itemsize 53 extent data disk bytenr 4334788608 nr 4096 extent data offset 0 nr 4096 ram 4096 The file extent item at offset 659456 (item 15) ends at offset 823296 (659456 + 163840) while the next file extent item (item 16) starts at offset 663552. Another different problem that the race can trigger is a failure in the assertions at tree-log.c:copy_items(), which expect that the first file extent item key we found before releasing the path exists after we have released path and that the last key we found before releasing the path also exists after releasing the path: $ cat -n fs/btrfs/tree-log.c 4080 if (need_find_last_extent) { 4081 /* btrfs_prev_leaf could return 1 without releasing the path */ 4082 btrfs_release_path(src_path); 4083 ret = btrfs_search_slot(NULL, inode->root, &first_key, 4084 src_path, 0, 0); 4085 if (ret < 0) 4086 return ret; 4087 ASSERT(ret == 0); (...) 4103 if (i >= btrfs_header_nritems(src_path->nodes[0])) { 4104 ret = btrfs_next_leaf(inode->root, src_path); 4105 if (ret < 0) 4106 return ret; 4107 ASSERT(ret == 0); 4108 src = src_path->nodes[0]; 4109 i = 0; 4110 need_find_last_extent = true; 4111 } (...) The second assertion implicitly expects that the last key before the path release still exists, because the surrounding while loop only stops after we have found that key. When this assertion fails it produces a stack like this: [139590.037075] assertion failed: ret == 0, file: fs/btrfs/tree-log.c, line: 4107 [139590.037406] ------------[ cut here ]------------ [139590.037707] kernel BUG at fs/btrfs/ctree.h:3546! [139590.038034] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC PTI [139590.038340] CPU: 1 PID: 31841 Comm: fsstress Tainted: G W 5.0.0-btrfs-next-46 #1 (...) [139590.039354] RIP: 0010:assfail.constprop.24+0x18/0x1a [btrfs] (...) [139590.040397] RSP: 0018:ffffa27f48f2b9b0 EFLAGS: 00010282 [139590.040730] RAX: 0000000000000041 RBX: ffff897c635d92c8 RCX: 0000000000000000 [139590.041105] RDX: 0000000000000000 RSI: ffff897d36a96868 RDI: ffff897d36a96868 [139590.041470] RBP: ffff897d1b9a0708 R08: 0000000000000000 R09: 0000000000000000 [139590.041815] R10: 0000000000000008 R11: 0000000000000000 R12: 0000000000000013 [139590.042159] R13: 0000000000000227 R14: ffff897cffcbba88 R15: 0000000000000001 [139590.042501] FS: 00007f2efc8dee80(0000) GS:ffff897d36a80000(0000) knlGS:0000000000000000 [139590.042847] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [139590.043199] CR2: 00007f8c064935e0 CR3: 0000000232252002 CR4: 00000000003606e0 [139590.043547] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [139590.043899] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [139590.044250] Call Trace: [139590.044631] copy_items+0xa3f/0x1000 [btrfs] [139590.045009] ? generic_bin_search.constprop.32+0x61/0x200 [btrfs] [139590.045396] btrfs_log_inode+0x7b3/0xd70 [btrfs] [139590.045773] btrfs_log_inode_parent+0x2b3/0xce0 [btrfs] [139590.046143] ? do_raw_spin_unlock+0x49/0xc0 [139590.046510] btrfs_log_dentry_safe+0x4a/0x70 [btrfs] [139590.046872] btrfs_sync_file+0x3b6/0x440 [btrfs] [139590.047243] btrfs_file_write_iter+0x45b/0x5c0 [btrfs] [139590.047592] __vfs_write+0x129/0x1c0 [139590.047932] vfs_write+0xc2/0x1b0 [139590.048270] ksys_write+0x55/0xc0 [139590.048608] do_syscall_64+0x60/0x1b0 [139590.048946] entry_SYSCALL_64_after_hwframe+0x49/0xbe [139590.049287] RIP: 0033:0x7f2efc4be190 (...) [139590.050342] RSP: 002b:00007ffe743243a8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 [139590.050701] RAX: ffffffffffffffda RBX: 0000000000008d58 RCX: 00007f2efc4be190 [139590.051067] RDX: 0000000000008d58 RSI: 00005567eca0f370 RDI: 0000000000000003 [139590.051459] RBP: 0000000000000024 R08: 0000000000000003 R09: 0000000000008d60 [139590.051863] R10: 0000000000000078 R11: 0000000000000246 R12: 0000000000000003 [139590.052252] R13: 00000000003d3507 R14: 00005567eca0f370 R15: 0000000000000000 (...) [139590.055128] ---[ end trace 193f35d0215cdeeb ]--- So fix this race between a full ranged fsync and writeback of adjacent ranges by flushing all delalloc and waiting for all ordered extents to complete before logging the inode. This is the simplest way to solve the problem because currently the full fsync path does not deal with ranges at all (it assumes a full range from 0 to LLONG_MAX) and it always needs to look at adjacent ranges for hole detection. For use cases of ranged fsyncs this can make a few fsyncs slower but on the other hand it can make some following fsyncs to other ranges do less work or no need to do anything at all. A full fsync is rare anyway and happens only once after loading/creating an inode and once after less common operations such as a shrinking truncate. This is an issue that exists for a long time, and was often triggered by generic/127, because it does mmap'ed writes and msync (which triggers a ranged fsync). Adding support for the tree checker to detect overlapping extents (next patch in the series) and trigger a WARN() when such cases are found, and then calling btrfs_check_leaf_full() at the end of btrfs_insert_file_extent() made the issue much easier to detect. Running btrfs/072 with that change to the tree checker and making fsstress open files always with O_SYNC made it much easier to trigger the issue (as triggering it with generic/127 is very rare). CC: stable@vger.kernel.org # 3.16+ Reviewed-by:Josef Bacik <josef@toxicpanda.com> Signed-off-by:
Filipe Manana <fdmanana@suse.com> Signed-off-by:
David Sterba <dsterba@suse.com> Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Showing
Please register or sign in to comment