[PATCH] ext4: flush s_error_work before journal destroy in ext4_fill_super

[yangerkun <yangerkun@huawei.com>]

'commit c92dc856848f ("ext4: defer saving error info from atomic
context")' and '2d01ddc86606 ("ext4: save error info to sb through journal
if available")' add s_error_work to fix checksum error problem. But the
error path in ext4_fill_super can lead the follow BUG_ON.

Our testcase got follow BUG:
[32031.759805] ------------[ cut here ]------------
[32031.759807] kernel BUG at fs/jbd2/transaction.c:373!
[32031.760075] invalid opcode: 0000 [#1] SMP PTI
[32031.760336] CPU: 5 PID: 1029268 Comm: kworker/5:1 Kdump: loaded
Tainted: G           OE    --------- -  -
4.18.0
...
[32031.766665]  jbd2__journal_start+0xf1/0x1f0 [jbd2]
[32031.766934]  jbd2_journal_start+0x19/0x20 [jbd2]
[32031.767218]  flush_stashed_error_work+0x30/0x90 [ext4]
[32031.767487]  process_one_work+0x195/0x390
[32031.767747]  worker_thread+0x30/0x390
[32031.768007]  ? process_one_work+0x390/0x390
[32031.768265]  kthread+0x10d/0x130
[32031.768521]  ? kthread_flush_work_fn+0x10/0x10
[32031.768778]  ret_from_fork+0x35/0x40

static int start_this_handle(...)
    BUG_ON(journal->j_flags & JBD2_UNMOUNT); <---- Trigger this

flush_stashed_error_work will try to access journal. We cannot flush
s_error_work after journal destroy.

Fixes: c92dc856848f ("ext4: defer saving error info from atomic context")
Fixes: 2d01ddc86606 ("ext4: save error info to sb through journal if available")
Signed-off-by: yangerkun <yangerkun@huawei.com>
---
 fs/ext4/super.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index dfa09a277b56..7db2be03848f 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5173,15 +5173,15 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 
 	ext4_xattr_destroy_cache(sbi->s_ea_block_cache);
 	sbi->s_ea_block_cache = NULL;
+failed_mount3a:
+	ext4_es_unregister_shrinker(sbi);
+failed_mount3:
+	flush_work(&sbi->s_error_work);
 
 	if (sbi->s_journal) {
 		jbd2_journal_destroy(sbi->s_journal);
 		sbi->s_journal = NULL;
 	}
-failed_mount3a:
-	ext4_es_unregister_shrinker(sbi);
-failed_mount3:
-	flush_work(&sbi->s_error_work);
 	del_timer_sync(&sbi->s_err_report);
 	ext4_stop_mmpd(sbi);
 failed_mount2:
-- 
2.31.1