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md: close a race with setting mddev->in_sync 

If ->in_sync is being set just as md_write_start() is being called,
it is possible that set_in_sync() won't see the elevated
->writes_pending, and md_write_start() won't see the set ->in_sync.

To close this race, re-test ->writes_pending after setting ->in_sync,
and add memory barriers to ensure the increment of ->writes_pending
will be seen by the time of this second test, or the new ->in_sync
will be seen by md_write_start().

Add a spinlock to array_state_show() to ensure this temporary
instability is never visible from userspace.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>
This commit is contained in:
NeilBrown 2017-03-15 14:05:14 +11:00 committed by Shaohua Li
parent 6497709b5d
commit 55cc39f345
1 changed files with 7 additions and 0 deletions
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7
drivers/md/md.c
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@ -2258,6 +2258,10 @@ static bool set_in_sync(struct mddev *mddev)
if (atomic_read(&mddev->writes_pending) == 0) {
if (mddev->in_sync == 0) {
mddev->in_sync = 1;
smp_mb();
if (atomic_read(&mddev->writes_pending))
/* lost a race with md_write_start() */
mddev->in_sync = 0;
set_bit(MD_SB_CHANGE_CLEAN, &mddev->sb_flags);
sysfs_notify_dirent_safe(mddev->sysfs_state);
}
@ -4011,6 +4015,7 @@ array_state_show(struct mddev *mddev, char *page)
st = read_auto;
break;
case 0:
spin_lock(&mddev->lock);
if (test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags))
st = write_pending;
else if (mddev->in_sync)
@ -4019,6 +4024,7 @@ array_state_show(struct mddev *mddev, char *page)
st = active_idle;
else
st = active;
spin_unlock(&mddev->lock);
}
else {
if (list_empty(&mddev->disks) &&
@ -7885,6 +7891,7 @@ void md_write_start(struct mddev *mddev, struct bio *bi)
did_change = 1;
}
atomic_inc(&mddev->writes_pending);
smp_mb(); /* Match smp_mb in set_in_sync() */
if (mddev->safemode == 1)
mddev->safemode = 0;
if (mddev->in_sync) {