linux-ext4 - [PATCH -next v2 4/6] ext4: avoid to re-read mmp check data get from page cache

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Date:   Sat, 11 Sep 2021 17:00:57 +0800
From:   Ye Bin <yebin10@...wei.com>
To:     <tytso@....edu>, <adilger.kernel@...ger.ca>,
        <linux-ext4@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <jack@...e.cz>,
        Ye Bin <yebin10@...wei.com>
Subject: [PATCH -next v2 4/6] ext4: avoid to re-read mmp check data get from page cache

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>
---
 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 4433fe7e9e86..007bde3c12b8 100644
--- a/fs/ext4/mmp.c
+++ b/fs/ext4/mmp.c
@@ -213,10 +213,7 @@ static int kmmpd(void *data)
 		 * we need to check if the MMP block is as we write it.
 		 */
 		if (jiffies - last_check_time > mmp_check_interval * HZ) {
-			struct buffer_head *bh_check = NULL;
-			struct mmp_struct *mmp_check;
-
-			retval = read_mmp_block(sb, &bh_check, mmp_block);
+			retval = read_mmp_block(sb, &bh, mmp_block);
 			if (retval) {
 				ext4_error_err(sb, -retval,
 					       "error reading MMP data: %d",
@@ -224,20 +221,18 @@ 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);
 			last_check_time = jiffies;
 		}
 
-- 
2.31.1