On 2021/10/7 20:26, Jan Kara wrote:
On Sat 11-09-21 17:00:54, Ye Bin wrote:
If two host has the same nodename, and seq start from 0, May cause the
detection mechanism to fail.
So init seq with random value to accelerate conflict detection.
Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
Thanks for the patch. I agree the code in kmmpd looks suspicious. The
sequence number is initialized to a random number in
ext4_multi_mount_protect() which is called before kmmpd is started. I think
kmmpd() should initialize its 'seq' to a number fetched from the mmp
block, instead of 0 as is currently in the code. I don't think generating a
new random number as you do is really needed...
Honza
Thank you for your advice，i will fix it.
---
fs/ext4/mmp.c | 32 ++++++++++++++++----------------
1 file changed, 16 insertions(+), 16 deletions(-)
diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
index cebea4270817..12af6dc8457b 100644
--- a/fs/ext4/mmp.c
+++ b/fs/ext4/mmp.c
@@ -122,6 +122,21 @@ void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
(int)sizeof(mmp->mmp_bdevname), mmp->mmp_bdevname);
}
+/*
+ * Get a random new sequence number but make sure it is not greater than
+ * EXT4_MMP_SEQ_MAX.
+ */
+static unsigned int mmp_new_seq(void)
+{
+ u32 new_seq;
+
+ do {
+ new_seq = prandom_u32();
+ } while (new_seq > EXT4_MMP_SEQ_MAX);
+
+ return new_seq;
+}
+
/*
* kmmpd will update the MMP sequence every s_mmp_update_interval seconds
*/
@@ -132,7 +147,7 @@ static int kmmpd(void *data)
struct buffer_head *bh = EXT4_SB(sb)->s_mmp_bh;
struct mmp_struct *mmp;
ext4_fsblk_t mmp_block;
- u32 seq = 0;
+ u32 seq = mmp_new_seq();
unsigned long failed_writes = 0;
int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
unsigned mmp_check_interval;
@@ -258,21 +273,6 @@ void ext4_stop_mmpd(struct ext4_sb_info *sbi)
}
}
-/*
- * Get a random new sequence number but make sure it is not greater than
- * EXT4_MMP_SEQ_MAX.
- */
-static unsigned int mmp_new_seq(void)
-{
- u32 new_seq;
-
- do {
- new_seq = prandom_u32();
- } while (new_seq > EXT4_MMP_SEQ_MAX);
-
- return new_seq;
-}
-
/*
* Protect the filesystem from being mounted more than once.
*/
--
2.31.1
