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Commit be481881 authored by Li Nan's avatar Li Nan Committed by Greg Kroah-Hartman
Browse files

md/raid10: fix io loss while replacement replace rdev 



[ Upstream commit 2ae6aaf76912bae53c74b191569d2ab484f24bf3 ]

When removing a disk with replacement, the replacement will be used to
replace rdev. During this process, there is a brief window in which both
rdev and replacement are read as NULL in raid10_write_request(). This
will result in io not being submitted but it should be.

  //remove				//write
  raid10_remove_disk			raid10_write_request
   mirror->rdev = NULL
					 read rdev -> NULL
   mirror->rdev = mirror->replacement
   mirror->replacement = NULL
					 read replacement -> NULL

Fix it by reading replacement first and rdev later, meanwhile, use smp_mb()
to prevent memory reordering.

Fixes: 475b0321 ("md/raid10: writes should get directed to replacement as well as original.")
Signed-off-by: default avatarLi Nan <linan122@huawei.com>
Reviewed-by: default avatarYu Kuai <yukuai3@huawei.com>
Signed-off-by: default avatarSong Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230602091839.743798-3-linan666@huaweicloud.com


Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 45fa023b

drivers/md/raid10.c

+18 −4
Original line number Diff line number Diff line
@@ -751,8 +751,16 @@ static struct md_rdev *read_balance(struct r10conf *conf, 
		disk = r10_bio->devs[slot].devnum;

		rdev = rcu_dereference(conf->mirrors[disk].replacement);

		if (rdev == NULL || test_bit(Faulty, &rdev->flags) ||

		    r10_bio->devs[slot].addr + sectors > rdev->recovery_offset)

		    r10_bio->devs[slot].addr + sectors >

		    rdev->recovery_offset) {

			/*

			 * Read replacement first to prevent reading both rdev

			 * and replacement as NULL during replacement replace

			 * rdev.

			 */

			smp_mb();

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

		}

		if (rdev == NULL ||

		    test_bit(Faulty, &rdev->flags))

			continue;
@@ -1363,9 +1371,15 @@ static void raid10_write_request(struct mddev *mddev, struct bio *bio, 


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

		int d = r10_bio->devs[i].devnum;

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

		struct md_rdev *rrdev = rcu_dereference(

			conf->mirrors[d].replacement);

		struct md_rdev *rdev, *rrdev;



		rrdev = rcu_dereference(conf->mirrors[d].replacement);

		/*

		 * Read replacement first to prevent reading both rdev and

		 * replacement as NULL during replacement replace rdev.

		 */

		smp_mb();

		rdev = rcu_dereference(conf->mirrors[d].rdev);

		if (rdev == rrdev)

			rrdev = NULL;

		if (rdev && unlikely(test_bit(Blocked, &rdev->flags))) {