On 2021/10/8 9:56, yebin wrote:
On 2021/10/7 20:31, Jan Kara wrote:
On Sat 11-09-21 17:00:55, Ye Bin wrote:
kmmpd:
...
diff = jiffies - last_update_time;
if (diff > mmp_check_interval * HZ) {
...
As "mmp_check_interval = 2 * mmp_update_interval", 'diff' always little
than 'mmp_update_interval', so there will never trigger detection.
Introduce last_check_time record previous check time.
Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
I think the check is there only for the case where write_mmp_block() +
sleep took longer than mmp_check_interval. I agree that should rarely
happen but on a really busy system it is possible and in that case we
would
miss updating mmp block for too long and so another node could have
started
using the filesystem. I actually don't see a reason why kmmpd should be
checking the block each mmp_check_interval as you do -
mmp_check_interval
is just for ext4_multi_mount_protect() to know how long it should wait
before considering mmp block stale... Am I missing something?
Honza
I'm sorry, I didn't understand the detection mechanism here before.
Now I understand
the detection mechanism here.
As you said, it's just an abnormal protection. There's really no problem.
Yeah, i did test as following steps
hostA hostB
mount
ext4_multi_mount_protect -> seq == EXT4_MMP_SEQ_CLEAN
delay 5s after label "skip" so hostB will see seq is
EXT4_MMP_SEQ_CLEAN
mount
ext4_multi_mount_protect -> seq ==
EXT4_MMP_SEQ_CLEAN
run kmmpd
run kmmpd
Actually，in this situation kmmpd will not detect confliction.
In ext4_multi_mount_protect function we write mmp data fisrt and wait
'wait_time * HZ' seconds,
read mmp data do check.Most of the time, If 'wait_time' is zero, it can
pass check.
---
fs/ext4/mmp.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
index 12af6dc8457b..c781b09a78c9 100644
--- a/fs/ext4/mmp.c
+++ b/fs/ext4/mmp.c
@@ -152,6 +152,7 @@ static int kmmpd(void *data)
int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
unsigned mmp_check_interval;
unsigned long last_update_time;
+ unsigned long last_check_time;
unsigned long diff;
int retval = 0;
@@ -170,6 +171,7 @@ static int kmmpd(void *data)
memcpy(mmp->mmp_nodename, init_utsname()->nodename,
sizeof(mmp->mmp_nodename));
+ last_check_time = jiffies;
while (!kthread_should_stop() && !sb_rdonly(sb)) {
if (!ext4_has_feature_mmp(sb)) {
@@ -198,17 +200,18 @@ static int kmmpd(void *data)
}
diff = jiffies - last_update_time;
- if (diff < mmp_update_interval * HZ)
+ if (diff < mmp_update_interval * HZ) {
schedule_timeout_interruptible(mmp_update_interval *
HZ - diff);
+ diff = jiffies - last_update_time;
+ }
/*
* We need to make sure that more than mmp_check_interval
- * seconds have not passed since writing. If that has happened
- * we need to check if the MMP block is as we left it.
+ * seconds have not passed since check. If that has happened
+ * we need to check if the MMP block is as we write it.
*/
- diff = jiffies - last_update_time;
- if (diff > mmp_check_interval * HZ) {
+ if (jiffies - last_check_time > mmp_check_interval * HZ) {
struct buffer_head *bh_check = NULL;
struct mmp_struct *mmp_check;
@@ -234,6 +237,7 @@ static int kmmpd(void *data)
goto wait_to_exit;
}
put_bh(bh_check);
+ last_check_time = jiffies;
}
/*
--
2.31.1
