From: Boris Burkov <boris@xxxxxx>
commit 4eb4e85c4f818491efc67e9373aa16b123c3f522 upstream.
If inc_block_group_ro systematically fails (e.g. due to ETXTBUSY from
swap) or btrfs_relocate_chunk systematically fails (from lack of
space), then this worker becomes an infinite loop.
At the very least, this strands the cleaner thread, but can also result
in hung tasks/RCU stalls on PREEMPT_NONE kernels and if the
reclaim_bgs_lock mutex is not contended.
I believe the best long term fix is to manage reclaim via work queue,
where we queue up a relocation on the triggering condition and re-queue
on failure. In the meantime, this is an easy fix to apply to avoid the
immediate pain.
Fixes: 7e2718099438 ("btrfs: reinsert BGs failed to reclaim")
CC: stable@xxxxxxxxxxxxxxx # 6.6+
Signed-off-by: Boris Burkov <boris@xxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/block-group.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1615,6 +1615,7 @@ void btrfs_reclaim_bgs_work(struct work_
container_of(work, struct btrfs_fs_info, reclaim_bgs_work);
struct btrfs_block_group *bg;
struct btrfs_space_info *space_info;
+ LIST_HEAD(retry_list);
if (!test_bit(BTRFS_FS_OPEN, &fs_info->flags))
return;
@@ -1717,8 +1718,11 @@ void btrfs_reclaim_bgs_work(struct work_
}
next:
- if (ret)
- btrfs_mark_bg_to_reclaim(bg);
+ if (ret) {
+ /* Refcount held by the reclaim_bgs list after splice. */
+ btrfs_get_block_group(bg);
+ list_add_tail(&bg->bg_list, &retry_list);
+ }
btrfs_put_block_group(bg);
mutex_unlock(&fs_info->reclaim_bgs_lock);
@@ -1738,6 +1742,9 @@ next:
spin_unlock(&fs_info->unused_bgs_lock);
mutex_unlock(&fs_info->reclaim_bgs_lock);
end:
+ spin_lock(&fs_info->unused_bgs_lock);
+ list_splice_tail(&retry_list, &fs_info->reclaim_bgs);
+ spin_unlock(&fs_info->unused_bgs_lock);
btrfs_exclop_finish(fs_info);
sb_end_write(fs_info->sb);
}
Patches currently in stable-queue which might be from boris@xxxxxx are
queue-6.1/btrfs-retry-block-group-reclaim-without-infinite-loop.patch
