Commit 7ecab28c authored by Yu Kuai's avatar Yu Kuai Committed by Song Liu
Browse files

md/md-multipath: remove rcu protection to access rdev from conf 



Because it's safe to accees rdev from conf:
 - If any spinlock is held, because synchronize_rcu() from
   md_kick_rdev_from_array() will prevent 'rdev' to be freed until
   spinlock is released;
 - If there is normal IO inflight, because mddev_suspend() will prevent
   rdev to be added or removed from array;

And these will cover all the scenarios in md-multipath.

Signed-off-by: default avatarYu Kuai <yukuai3@huawei.com>
Signed-off-by: default avatarSong Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231125081604.3939938-6-yukuai1@huaweicloud.com
parent ad860670

drivers/md/md-multipath.c

+12 −11
Original line number Diff line number Diff line
@@ -32,17 +32,15 @@ static int multipath_map (struct mpconf *conf) 
	 * now we use the first available disk.

	 */



	rcu_read_lock();

	for (i = 0; i < disks; i++) {

		struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);

		struct md_rdev *rdev = conf->multipaths[i].rdev;



		if (rdev && test_bit(In_sync, &rdev->flags) &&

		    !test_bit(Faulty, &rdev->flags)) {

			atomic_inc(&rdev->nr_pending);

			rcu_read_unlock();

			return i;

		}

	}

	rcu_read_unlock();



	pr_crit_ratelimited("multipath_map(): no more operational IO paths?\n");

	return (-1);
@@ -137,14 +135,16 @@ static void multipath_status(struct seq_file *seq, struct mddev *mddev) 
	struct mpconf *conf = mddev->private;

	int i;



	lockdep_assert_held(&mddev->lock);



	seq_printf (seq, " [%d/%d] [", conf->raid_disks,

		    conf->raid_disks - mddev->degraded);

	rcu_read_lock();

	for (i = 0; i < conf->raid_disks; i++) {

		struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);

		seq_printf (seq, "%s", rdev && test_bit(In_sync, &rdev->flags) ? "U" : "_");

		struct md_rdev *rdev = READ_ONCE(conf->multipaths[i].rdev);



		seq_printf(seq, "%s",

			   rdev && test_bit(In_sync, &rdev->flags) ? "U" : "_");

	}

	rcu_read_unlock();

	seq_putc(seq, ']');

}
@@ -195,6 +195,7 @@ static void print_multipath_conf (struct mpconf *conf) 
	pr_debug(" --- wd:%d rd:%d\n", conf->raid_disks - conf->mddev->degraded,

		 conf->raid_disks);



	lockdep_assert_held(&conf->mddev->reconfig_mutex);

	for (i = 0; i < conf->raid_disks; i++) {

		tmp = conf->multipaths + i;

		if (tmp->rdev)
@@ -231,7 +232,7 @@ static int multipath_add_disk(struct mddev *mddev, struct md_rdev *rdev) 
			rdev->raid_disk = path;

			set_bit(In_sync, &rdev->flags);

			spin_unlock_irq(&conf->device_lock);

			rcu_assign_pointer(p->rdev, rdev);

			WRITE_ONCE(p->rdev, rdev);

			err = 0;

			break;

		}
@@ -257,7 +258,7 @@ static int multipath_remove_disk(struct mddev *mddev, struct md_rdev *rdev) 
			err = -EBUSY;

			goto abort;

		}

		p->rdev = NULL;

		WRITE_ONCE(p->rdev, NULL);

		err = md_integrity_register(mddev);

	}

abort: