Commit 46d4703b authored by Xiao Ni's avatar Xiao Ni Committed by Song Liu
Browse files

md/raid10: Remove unnecessary rcu_dereference in raid10_handle_discard 



We are seeing the following warning in raid10_handle_discard.
[  695.110751] =============================
[  695.131439] WARNING: suspicious RCU usage
[  695.151389] 4.18.0-319.el8.x86_64+debug #1 Not tainted
[  695.174413] -----------------------------
[  695.192603] drivers/md/raid10.c:1776 suspicious
rcu_dereference_check() usage!
[  695.225107] other info that might help us debug this:
[  695.260940] rcu_scheduler_active = 2, debug_locks = 1
[  695.290157] no locks held by mkfs.xfs/10186.

In the first loop of function raid10_handle_discard. It already
determines which disk need to handle discard request and add the
rdev reference count rdev->nr_pending. So the conf->mirrors will
not change until all bios come back from underlayer disks. It
doesn't need to use rcu_dereference to get rdev.

Cc: stable@vger.kernel.org
Fixes: d30588b2 ('md/raid10: improve raid10 discard request')
Signed-off-by: default avatarXiao Ni <xni@redhat.com>
Acked-by: default avatarGuoqing Jiang <guoqing.jiang@linux.dev>
Signed-off-by: default avatarSong Liu <songliubraving@fb.com>
parent 7ee656c3

drivers/md/raid10.c

+10 −4
Original line number Diff line number Diff line
@@ -1712,6 +1712,11 @@ static int raid10_handle_discard(struct mddev *mddev, struct bio *bio) 
	} else

		r10_bio->master_bio = (struct bio *)first_r10bio;



	/*

	 * first select target devices under rcu_lock and

	 * inc refcount on their rdev.  Record them by setting

	 * bios[x] to bio

	 */

	rcu_read_lock();

	for (disk = 0; disk < geo->raid_disks; disk++) {

		struct md_rdev *rdev = rcu_dereference(conf->mirrors[disk].rdev);
@@ -1743,9 +1748,6 @@ static int raid10_handle_discard(struct mddev *mddev, struct bio *bio) 
	for (disk = 0; disk < geo->raid_disks; disk++) {

		sector_t dev_start, dev_end;

		struct bio *mbio, *rbio = NULL;

		struct md_rdev *rdev = rcu_dereference(conf->mirrors[disk].rdev);

		struct md_rdev *rrdev = rcu_dereference(

			conf->mirrors[disk].replacement);



		/*

		 * Now start to calculate the start and end address for each disk.
@@ -1775,9 +1777,12 @@ static int raid10_handle_discard(struct mddev *mddev, struct bio *bio) 


		/*

		 * It only handles discard bio which size is >= stripe size, so

		 * dev_end > dev_start all the time

		 * dev_end > dev_start all the time.

		 * It doesn't need to use rcu lock to get rdev here. We already

		 * add rdev->nr_pending in the first loop.

		 */

		if (r10_bio->devs[disk].bio) {

			struct md_rdev *rdev = conf->mirrors[disk].rdev;

			mbio = bio_clone_fast(bio, GFP_NOIO, &mddev->bio_set);

			mbio->bi_end_io = raid10_end_discard_request;

			mbio->bi_private = r10_bio;
@@ -1790,6 +1795,7 @@ static int raid10_handle_discard(struct mddev *mddev, struct bio *bio) 
			bio_endio(mbio);

		}

		if (r10_bio->devs[disk].repl_bio) {

			struct md_rdev *rrdev = conf->mirrors[disk].replacement;

			rbio = bio_clone_fast(bio, GFP_NOIO, &mddev->bio_set);

			rbio->bi_end_io = raid10_end_discard_request;

			rbio->bi_private = r10_bio;