linux-ext4 - Re: [RFC PATCH v3 2/8] jbd2: ensure abort the journal if detect IO error when writing original buffer back

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Date:   Thu, 3 Jun 2021 18:21:40 +0200
From:   Jan Kara <jack@...e.cz>
To:     Zhang Yi <yi.zhang@...wei.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, jack@...e.cz, yukuai3@...wei.com
Subject: Re: [RFC PATCH v3 2/8] jbd2: ensure abort the journal if detect IO
 error when writing original buffer back

On Thu 27-05-21 21:56:35, Zhang Yi wrote:
> Although we merged c044f3d8360 ("jbd2: abort journal if free a async
> write error metadata buffer"), there is a race between
> jbd2_journal_try_to_free_buffers() and jbd2_journal_destroy(), so the
> jbd2_log_do_checkpoint() may still fail to detect the buffer write
> io error flag which may lead to filesystem inconsistency.
> 
> jbd2_journal_try_to_free_buffers()     ext4_put_super()
>                                         jbd2_journal_destroy()
>   __jbd2_journal_remove_checkpoint()
>   detect buffer write error              jbd2_log_do_checkpoint()
>                                          jbd2_cleanup_journal_tail()
>                                            <--- lead to inconsistency
>   jbd2_journal_abort()
> 
> Fix this issue by introducing a new atomic flag which only have one
> JBD2_CHECKPOINT_IO_ERROR bit now, and set it in
> __jbd2_journal_remove_checkpoint() when freeing a checkpoint buffer
> which has write_io_error flag. Then jbd2_journal_destroy() will detect
> this mark and abort the journal to prevent updating log tail.
> 
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>

Looks good. Just one spelling fix below. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza
> @@ -575,6 +576,17 @@ int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
>  	journal = transaction->t_journal;
>  
>  	JBUFFER_TRACE(jh, "removing from transaction");
> +
> +	/*
> +	 * If we have failed to write the buffer out to disk, the filesystem
> +	 * may become inconsistent. We cannot abort the journal here since
> +	 * we hold j_list_lock and we have to careful about races with
					   ^^^ to be careful ...

> +	 * jbd2_journal_destroy(). So mark the writeback IO error in the
> +	 * journal here and we abort the journal later from a better context.
> +	 */
> +	if (buffer_write_io_error(bh))
> +		set_bit(JBD2_CHECKPOINT_IO_ERROR, &journal->j_atomic_flags);
> +
>  	__buffer_unlink(jh);
>  	jh->b_cp_transaction = NULL;
>  	jbd2_journal_put_journal_head(jh);
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR