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author | Filipe Manana <fdmanana@suse.com> | 2015-11-23 15:25:16 +0000 |
---|---|---|
committer | Chris Mason <clm@fb.com> | 2015-11-25 05:22:08 -0800 |
commit | 036a9348dcd0060e3df8f5b5db2a59e7d7eaf1f5 (patch) | |
tree | b771410f3850574d3559fcf99f73e6b1e8907171 | |
parent | 758f2dfcf8a249b1f1510aa32e625c2ec20642a3 (diff) | |
download | linux-036a9348dcd0060e3df8f5b5db2a59e7d7eaf1f5.tar.gz linux-036a9348dcd0060e3df8f5b5db2a59e7d7eaf1f5.tar.bz2 linux-036a9348dcd0060e3df8f5b5db2a59e7d7eaf1f5.zip |
Btrfs: fix race between cleaner kthread and space cache writeout
When a block group becomes unused and the cleaner kthread is currently
running, we can end up getting the current transaction aborted with error
-ENOENT when we try to commit the transaction, leading to the following
trace:
[59779.258768] WARNING: CPU: 3 PID: 5990 at fs/btrfs/extent-tree.c:3740 btrfs_write_dirty_block_groups+0x17c/0x214 [btrfs]()
[59779.272594] BTRFS: Transaction aborted (error -2)
(...)
[59779.291137] Call Trace:
[59779.291621] [<ffffffff812566f4>] dump_stack+0x4e/0x79
[59779.292543] [<ffffffff8104d0a6>] warn_slowpath_common+0x9f/0xb8
[59779.293435] [<ffffffffa04cb81f>] ? btrfs_write_dirty_block_groups+0x17c/0x214 [btrfs]
[59779.295000] [<ffffffff8104d107>] warn_slowpath_fmt+0x48/0x50
[59779.296138] [<ffffffffa04c2721>] ? write_one_cache_group.isra.32+0x77/0x82 [btrfs]
[59779.297663] [<ffffffffa04cb81f>] btrfs_write_dirty_block_groups+0x17c/0x214 [btrfs]
[59779.299141] [<ffffffffa0549b0d>] commit_cowonly_roots+0x1de/0x261 [btrfs]
[59779.300359] [<ffffffffa04dd5b6>] btrfs_commit_transaction+0x4c4/0x99c [btrfs]
[59779.301805] [<ffffffffa04b5df4>] btrfs_sync_fs+0x145/0x1ad [btrfs]
[59779.302893] [<ffffffff81196634>] sync_filesystem+0x7f/0x93
(...)
[59779.318186] ---[ end trace 577e2daff90da33a ]---
The following diagram illustrates a sequence of steps leading to this
problem:
CPU 1 CPU 2
<at transaction N>
adds bg A to list
fs_info->unused_bgs
adds bg B to list
fs_info->unused_bgs
<transaction kthread
commits transaction N
and wakes up the
cleaner kthread>
cleaner kthread
delete_unused_bgs()
sees bg A in list
fs_info->unused_bgs
btrfs_start_transaction()
<transaction N + 1 starts>
deletes bg A
update_block_group(bg C)
--> adds bg C to list
fs_info->unused_bgs
deletes bg B
sees bg C in the list
fs_info->unused_bgs
btrfs_remove_chunk(bg C)
btrfs_remove_block_group(bg C)
--> checks if the block group
is in a dirty list, and
because it isn't now, it
does nothing
--> the block group item
is deleted from the
extent tree
--> adds bg C to list
transaction->dirty_bgs
some task calls
btrfs_commit_transaction(t N + 1)
commit_cowonly_roots()
btrfs_write_dirty_block_groups()
--> sees bg C in cur_trans->dirty_bgs
--> calls write_one_cache_group()
which returns -ENOENT because
it did not find the block group
item in the extent tree
--> transaction aborte with -ENOENT
because write_one_cache_group()
returned that error
So fix this by adding a block group to the list of dirty block groups
before adding it to the list of unused block groups.
This happened on a stress test using fsstress plus concurrent calls to
fallocate 20G and truncate (releasing part of the space allocated with
fallocate).
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
-rw-r--r-- | fs/btrfs/extent-tree.c | 29 |
1 files changed, 16 insertions, 13 deletions
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 8fd14b6f1d33..e563e5ab72b4 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -5915,19 +5915,6 @@ static int update_block_group(struct btrfs_trans_handle *trans, set_extent_dirty(info->pinned_extents, bytenr, bytenr + num_bytes - 1, GFP_NOFS | __GFP_NOFAIL); - /* - * No longer have used bytes in this block group, queue - * it for deletion. - */ - if (old_val == 0) { - spin_lock(&info->unused_bgs_lock); - if (list_empty(&cache->bg_list)) { - btrfs_get_block_group(cache); - list_add_tail(&cache->bg_list, - &info->unused_bgs); - } - spin_unlock(&info->unused_bgs_lock); - } } spin_lock(&trans->transaction->dirty_bgs_lock); @@ -5939,6 +5926,22 @@ static int update_block_group(struct btrfs_trans_handle *trans, } spin_unlock(&trans->transaction->dirty_bgs_lock); + /* + * No longer have used bytes in this block group, queue it for + * deletion. We do this after adding the block group to the + * dirty list to avoid races between cleaner kthread and space + * cache writeout. + */ + if (!alloc && old_val == 0) { + spin_lock(&info->unused_bgs_lock); + if (list_empty(&cache->bg_list)) { + btrfs_get_block_group(cache); + list_add_tail(&cache->bg_list, + &info->unused_bgs); + } + spin_unlock(&info->unused_bgs_lock); + } + btrfs_put_block_group(cache); total -= num_bytes; bytenr += num_bytes; |