From: Filipe Manana <[email protected]>
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 <[email protected]>
---
fs/btrfs/extent-tree.c | 29 ++++++++++++++++-------------
1 file changed, 16 insertions(+), 13 deletions(-)
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 8fd14b6..e563e5a 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;
--
2.1.3
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