Re: [PATCH 06/14] jbd2: replace ll_rw_block()

From: Jan Kara <jack@suse.cz>
To: Zhang Yi <yi.zhang@huawei.com>
Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, cluster-devel@redhat.com,
	ntfs3@lists.linux.dev, ocfs2-devel@oss.oracle.com,
	reiserfs-devel@vger.kernel.org, jack@suse.cz, tytso@mit.edu,
	akpm@linux-foundation.org, axboe@kernel.dk,
	viro@zeniv.linux.org.uk, rpeterso@redhat.com,
	agruenba@redhat.com, almaz.alexandrovich@paragon-software.com,
	mark@fasheh.com, dushistov@mail.ru, hch@infradead.org,
	chengzhihao1@huawei.com, yukuai3@huawei.com
Subject: Re: [PATCH 06/14] jbd2: replace ll_rw_block()
Date: Wed, 31 Aug 2022 12:58:45 +0200	[thread overview]
Message-ID: <20220831105845.mwfkh2prb557ajyr@quack3> (raw)
In-Reply-To: <20220831072111.3569680-7-yi.zhang@huawei.com>

On Wed 31-08-22 15:21:03, Zhang Yi wrote:
> ll_rw_block() is not safe for the sync read path because it cannot
> guarantee that submitting read IO if the buffer has been locked. We
> could get false positive EIO after wait_on_buffer() if the buffer has
> been locked by others. So stop using ll_rw_block() in
> journal_get_superblock(). We also switch to new bh_readahead_batch()
> for the buffer array readahead path.
> 
> Signed-off-by: Zhang Yi <yi.zhang@huawei.com>

Looks good to me. Feel free to add:

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

								Honza

> ---
>  fs/jbd2/journal.c  |  7 +++----
>  fs/jbd2/recovery.c | 16 ++++++++++------
>  2 files changed, 13 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 6350d3857c89..5a903aae6aad 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -1893,15 +1893,14 @@ static int journal_get_superblock(journal_t *journal)
>  {
>  	struct buffer_head *bh;
>  	journal_superblock_t *sb;
> -	int err = -EIO;
> +	int err;
>  
>  	bh = journal->j_sb_buffer;
>  
>  	J_ASSERT(bh != NULL);
>  	if (!buffer_uptodate(bh)) {
> -		ll_rw_block(REQ_OP_READ, 1, &bh);
> -		wait_on_buffer(bh);
> -		if (!buffer_uptodate(bh)) {
> +		err = bh_read(bh, 0);
> +		if (err) {
>  			printk(KERN_ERR
>  				"JBD2: IO error reading journal superblock\n");
>  			goto out;
> diff --git a/fs/jbd2/recovery.c b/fs/jbd2/recovery.c
> index f548479615c6..ee56a30b71cf 100644
> --- a/fs/jbd2/recovery.c
> +++ b/fs/jbd2/recovery.c
> @@ -100,7 +100,7 @@ static int do_readahead(journal_t *journal, unsigned int start)
>  		if (!buffer_uptodate(bh) && !buffer_locked(bh)) {
>  			bufs[nbufs++] = bh;
>  			if (nbufs == MAXBUF) {
> -				ll_rw_block(REQ_OP_READ, nbufs, bufs);
> +				bh_readahead_batch(bufs, nbufs, 0);
>  				journal_brelse_array(bufs, nbufs);
>  				nbufs = 0;
>  			}
> @@ -109,7 +109,7 @@ static int do_readahead(journal_t *journal, unsigned int start)
>  	}
>  
>  	if (nbufs)
> -		ll_rw_block(REQ_OP_READ, nbufs, bufs);
> +		bh_readahead_batch(bufs, nbufs, 0);
>  	err = 0;
>  
>  failed:
> @@ -152,9 +152,14 @@ static int jread(struct buffer_head **bhp, journal_t *journal,
>  		return -ENOMEM;
>  
>  	if (!buffer_uptodate(bh)) {
> -		/* If this is a brand new buffer, start readahead.
> -                   Otherwise, we assume we are already reading it.  */
> -		if (!buffer_req(bh))
> +		/*
> +		 * If this is a brand new buffer, start readahead.
> +		 * Otherwise, we assume we are already reading it.
> +		 */
> +		bool need_readahead = !buffer_req(bh);
> +
> +		bh_read_nowait(bh, 0);
> +		if (need_readahead)
>  			do_readahead(journal, offset);
>  		wait_on_buffer(bh);
>  	}
> @@ -687,7 +692,6 @@ static int do_one_pass(journal_t *journal,
>  					mark_buffer_dirty(nbh);
>  					BUFFER_TRACE(nbh, "marking uptodate");
>  					++info->nr_replays;
> -					/* ll_rw_block(WRITE, 1, &nbh); */
>  					unlock_buffer(nbh);
>  					brelse(obh);
>  					brelse(nbh);
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR