linux-kernel - Re: [PATCH v2 06/14] jbd2: replace ll_rw

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Message-ID: <20220901155007.nelecqohvd4plqqy@quack3>
Date:   Thu, 1 Sep 2022 17:50:07 +0200
From:   Jan Kara <jack@...e.cz>
To:     Zhang Yi <yi.zhang@...wei.com>
Cc:     linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, cluster-devel@...hat.com,
        ntfs3@...ts.linux.dev, ocfs2-devel@....oracle.com,
        reiserfs-devel@...r.kernel.org, jack@...e.cz, tytso@....edu,
        akpm@...ux-foundation.org, axboe@...nel.dk,
        viro@...iv.linux.org.uk, rpeterso@...hat.com, agruenba@...hat.com,
        almaz.alexandrovich@...agon-software.com, mark@...heh.com,
        dushistov@...l.ru, hch@...radead.org, chengzhihao1@...wei.com,
        yukuai3@...wei.com
Subject: Re: [PATCH v2 06/14] jbd2: replace ll_rw_block()

On Thu 01-09-22 21:34:57, 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@...wei.com>

Looks good to me. Feel free to add:

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

								Honza

> ---
>  fs/jbd2/journal.c  | 15 ++++++---------
>  fs/jbd2/recovery.c | 16 ++++++++++------
>  2 files changed, 16 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 6350d3857c89..140b070471c0 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -1893,19 +1893,16 @@ 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)) {
> -			printk(KERN_ERR
> -				"JBD2: IO error reading journal superblock\n");
> -			goto out;
> -		}
> +	err = bh_read(bh, 0);
> +	if (err < 0) {
> +		printk(KERN_ERR
> +			"JBD2: IO error reading journal superblock\n");
> +		goto out;
>  	}
>  
>  	if (buffer_verified(bh))
> diff --git a/fs/jbd2/recovery.c b/fs/jbd2/recovery.c
> index f548479615c6..1f878c315b03 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(nbufs, bufs, 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(nbufs, bufs, 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@...e.com>
SUSE Labs, CR