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btrfs: retry block group reclaim without infinite loop

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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: 7e27180994 ("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>
This commit is contained in:
Boris Burkov 2024-06-07 12:50:14 -07:00 committed by David Sterba
parent f3a5367c67
commit 4eb4e85c4f
1 changed files with 9 additions and 2 deletions
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11
fs/btrfs/block-group.c
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@ -1785,6 +1785,7 @@ void btrfs_reclaim_bgs_work(struct 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;
@ -1921,8 +1922,11 @@ void btrfs_reclaim_bgs_work(struct 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);
@ -1942,6 +1946,9 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
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);
}