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md/raid10: fix io loss while replacement replace rdev

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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: 475b0321a4 ("md/raid10: writes should get directed to replacement as well as original.")
Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230602091839.743798-3-linan666@huaweicloud.com
This commit is contained in:
Li Nan 2023-06-02 17:18:39 +08:00 committed by Song Liu
parent 8d355a46c1
commit 2ae6aaf769
1 changed files with 18 additions and 4 deletions
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22
drivers/md/raid10.c
View file

@ -779,8 +779,16 @@ 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;
@ -1482,9 +1490,15 @@ 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 && (test_bit(Faulty, &rdev->flags)))