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
> ---
> 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
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
