linux-ext4 - Re: [PATCH -next v3 5/5] ext4: avoid to re-read mmp check data get from page cache

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Date:   Tue, 19 Oct 2021 11:10:24 +0200
From:   Jan Kara <jack@...e.cz>
To:     Ye Bin <yebin10@...wei.com>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        jack@...e.cz
Subject: Re: [PATCH -next v3 5/5] ext4: avoid to re-read mmp check data get
 from page cache

On Tue 19-10-21 14:49:59, Ye Bin wrote:
> As call read_mmp_block pass bh_check which value is NULL, then call
> sb_getblk to get buffer_head. But mmp_block's buffer_head is already exist
>  which also is uptodate. Lead to compare the same data.
> 
> Signed-off-by: Ye Bin <yebin10@...wei.com>

This patch needs to go earlier in the series - just after patch 2.
Otherwise the read_mmp_block() cleanup is not correct. Otherwise it looks
good, just some language corrections:

ext4: remove useless bh_check variable

Since we initialize 'bh_check' to NULL and pass it to read_mmp_block(), that
function will just call sb_getblk() which will just return the buffer_head
we have in 'bh'. So just remove the pointless 'bh_check' variable and use
'bh' directly.

With this fixed feel free to add:

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

								Honza

> ---
>  fs/ext4/mmp.c | 17 ++++++-----------
>  1 file changed, 6 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
> index 61c765c249b9..8018f6fb6ac2 100644
> --- a/fs/ext4/mmp.c
> +++ b/fs/ext4/mmp.c
> @@ -186,10 +186,7 @@ static int kmmpd(void *data)
>  		 */
>  		diff = jiffies - last_update_time;
>  		if (diff > mmp_check_interval * HZ) {
> -			struct buffer_head *bh_check = NULL;
> -			struct mmp_struct *mmp_check;
> -
> -			retval = read_mmp_block(sb, bh_check);
> +			retval = read_mmp_block(sb, bh);
>  			if (retval) {
>  				ext4_error_err(sb, -retval,
>  					       "error reading MMP data: %d",
> @@ -197,20 +194,18 @@ static int kmmpd(void *data)
>  				goto wait_to_exit;
>  			}
>  
> -			mmp_check = (struct mmp_struct *)(bh_check->b_data);
> -			if (seq != mmp_check->mmp_seq ||
> -			    memcmp(nodename, mmp_check->mmp_nodename,
> -				   sizeof(mmp->mmp_nodename))) {
> -				dump_mmp_msg(sb, mmp_check,
> +			mmp = (struct mmp_struct *)(bh->b_data);
> +			if (seq != le32_to_cpu(mmp->mmp_seq) ||
> +			    memcmp(nodename, mmp->mmp_nodename,
> +				    sizeof(nodename))) {
> +				dump_mmp_msg(sb, mmp,
>  					     "Error while updating MMP info. "
>  					     "The filesystem seems to have been"
>  					     " multiply mounted.");
>  				ext4_error_err(sb, EBUSY, "abort");
> -				put_bh(bh_check);
>  				retval = -EBUSY;
>  				goto wait_to_exit;
>  			}
> -			put_bh(bh_check);
>  		}
>  
>  		 /*
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR