| Message ID | 20210911090059.1876456-2-yebin10@huawei.com |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | Fix some issues about mmp | expand |
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@huawei.com> 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 >
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@huawei.com> > 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 >>
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. */
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@huawei.com> --- fs/ext4/mmp.c | 32 ++++++++++++++++---------------- 1 file changed, 16 insertions(+), 16 deletions(-)