5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Boris Burkov boris@bur.io
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@vger.kernel.org # 6.6+ Signed-off-by: Boris Burkov boris@bur.io Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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 @@ -1493,6 +1493,7 @@ 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; @@ -1583,8 +1584,11 @@ 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); @@ -1604,6 +1608,9 @@ 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); }