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Commit 55cc39f3 authored by NeilBrown's avatar NeilBrown Committed by Shaohua Li
Browse files

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: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarShaohua Li <shli@fb.com>
parent 6497709b

drivers/md/md.c

+7 −0
Original line number Diff line number Diff line
@@ -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) {