commit cb7ab02156e4 cause a following deadlock found by
xfstests,btrfs/011:
Thread1 is commiting transaction which is blocked at
btrfs_scrub_pause().
Thread2 is calling btrfs_file_aio_write() which has held
inode's @i_mutex and commit transaction(blocked because
Thread1 is committing transaction).
Thread3 is copy_nocow_page worker which will also try to
hold inode @i_mutex, so thread3 will wait Thread1 finished.
Thread4 is waiting pending workers finished which will wait
Thread3 finished. So the problem is like this:
Thread1--->Thread4--->Thread3--->Thread2---->Thread1
Deadlock happens! we fix it by letting Thread1 go firstly,
which means we won't block transaction commit while we are
waiting pending workers finished.
Reported-by: Qu Wenruo <quwen...@cn.fujitsu.com>
Signed-off-by: Wang Shilong <wangsl.f...@cn.fujitsu.com>
---
fs/btrfs/scrub.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 51c342b..f2f8803 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -2686,10 +2686,23 @@ int scrub_enumerate_chunks(struct scrub_ctx *sctx,
wait_event(sctx->list_wait,
atomic_read(&sctx->bios_in_flight) == 0);
- atomic_set(&sctx->wr_ctx.flush_all_writes, 0);
+ atomic_inc(&fs_info->scrubs_paused);
+ wake_up(&fs_info->scrub_pause_wait);
+
+ /*
+ * must be called before we decrease @scrub_paused.
+ * make sure we don't block transaction commit while
+ * we are waiting pending workers finished.
+ */
wait_event(sctx->list_wait,
atomic_read(&sctx->workers_pending) == 0);
- scrub_blocked_if_needed(fs_info);
+ atomic_set(&sctx->wr_ctx.flush_all_writes, 0);
+
+ mutex_lock(&fs_info->scrub_lock);
+ __scrub_blocked_if_needed(fs_info);
+ atomic_dec(&fs_info->scrubs_paused);
+ mutex_unlock(&fs_info->scrub_lock);
+ wake_up(&fs_info->scrub_pause_wait);
btrfs_put_block_group(cache);
if (ret)
--
1.8.3.1
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