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Commit f97fcad3 authored by NeilBrown's avatar NeilBrown
Browse files

md: remove need for mddev_lock() in md_seq_show() 



The only access in md_seq_show that could suffer from races
not protected by ->lock is walking the rdev list.
This can receive sufficient protection from 'rcu'.

So use rdev_for_each_rcu() and get rid of mddev_lock().

Now reading /proc/mdstat will never block in md_seq_show.

Signed-off-by: default avatarNeilBrown <neilb@suse.de>
parent 978a7a47

drivers/md/md.c

+3 −5
Original line number Diff line number Diff line
@@ -6950,9 +6950,6 @@ static int md_seq_show(struct seq_file *seq, void *v) 
		return 0;

	}



	if (mddev_lock(mddev) < 0)

		return -EINTR;



	spin_lock(&mddev->lock);

	if (mddev->pers || mddev->raid_disks || !list_empty(&mddev->disks)) {

		seq_printf(seq, "%s : %sactive", mdname(mddev),
@@ -6966,7 +6963,8 @@ static int md_seq_show(struct seq_file *seq, void *v) 
		}



		sectors = 0;

		rdev_for_each(rdev, mddev) {

		rcu_read_lock();

		rdev_for_each_rcu(rdev, mddev) {

			char b[BDEVNAME_SIZE];

			seq_printf(seq, " %s[%d]",

				bdevname(rdev->bdev,b), rdev->desc_nr);
@@ -6982,6 +6980,7 @@ static int md_seq_show(struct seq_file *seq, void *v) 
				seq_printf(seq, "(R)");

			sectors += rdev->sectors;

		}

		rcu_read_unlock();



		if (!list_empty(&mddev->disks)) {

			if (mddev->pers)
@@ -7025,7 +7024,6 @@ static int md_seq_show(struct seq_file *seq, void *v) 
		seq_printf(seq, "\n");

	}

	spin_unlock(&mddev->lock);

	mddev_unlock(mddev);



	return 0;

}