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Subject: Re: [PATCH v2] ext4: flush s_error_work before journal destroy in
 ext4_fill_super
To:     <tytso@mit.edu>, <jack@suse.cz>
CC:     <linux-ext4@vger.kernel.org>, <yukuai3@huawei.com>
References: <20210831120449.2910005-1-yangerkun@huawei.com>
From:   yangerkun <yangerkun@huawei.com>
Message-ID: <7843daee-6de9-c684-9d11-1b4e1a90fbec@huawei.com>
Date:   Mon, 13 Sep 2021 14:22:27 +0800
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ping...

在 2021/8/31 20:04, yangerkun 写道:
> The error path in ext4_fill_super forget to flush s_error_work before
> journal destroy, and it may trigger the follow bug since
> flush_stashed_error_work can run concurrently with journal destroy
> without any protection for sbi->s_journal.
> 
> [32031.740193] EXT4-fs (loop66): get root inode failed
> [32031.740484] EXT4-fs (loop66): mount failed
> [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
> 4.18.0
> [32031.765112] Call Trace:
> [32031.765375]  ? __switch_to_asm+0x35/0x70
> [32031.765635]  ? __switch_to_asm+0x41/0x70
> [32031.765893]  ? __switch_to_asm+0x35/0x70
> [32031.766148]  ? __switch_to_asm+0x41/0x70
> [32031.766405]  ? _cond_resched+0x15/0x40
> [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
> 
> Besides, after we enable fast commit, ext4_fc_replay can add work to
> s_error_work but return success, so the latter journal destroy in
> ext4_load_journal can trigger this problem too.
> 
> Fix this problem with two steps:
> 1. Call ext4_commit_super directly in ext4_handle_error for the case
>     that called from ext4_fc_replay
> 2. Since it's hard to pair the init and flush for s_error_work, we'd
>     better add a extras flush_work before journal destroy in
>     ext4_fill_super
> 
> 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 | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index d6df62fc810c..06b5ad34d892 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -659,7 +659,7 @@ static void ext4_handle_error(struct super_block *sb, bool force_ro, int error,
>   		 * constraints, it may not be safe to do it right here so we
>   		 * defer superblock flushing to a workqueue.
>   		 */
> -		if (continue_fs)
> +		if (continue_fs && journal)
>   			schedule_work(&EXT4_SB(sb)->s_error_work);
>   		else
>   			ext4_commit_super(sb);
> @@ -5172,12 +5172,15 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>   	sbi->s_ea_block_cache = NULL;
>   
>   	if (sbi->s_journal) {
> +		/* flush s_error_work before journal destroy. */
> +		flush_work(&sbi->s_error_work);
>   		jbd2_journal_destroy(sbi->s_journal);
>   		sbi->s_journal = NULL;
>   	}
>   failed_mount3a:
>   	ext4_es_unregister_shrinker(sbi);
>   failed_mount3:
> +	/* flush s_error_work before sbi destroy */
>   	flush_work(&sbi->s_error_work);
>   	del_timer_sync(&sbi->s_err_report);
>   	ext4_stop_mmpd(sbi);
>