Re: [PATCH 3/3] md/raid10: fix io loss while replacement replace rdev
From: Yu Kuai <hidden>
Date: 2023-05-22 13:03:20
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Hi, 在 2023/05/22 19:54, linan666@huaweicloud.com 写道:
From: Li Nan <redacted> When we remove a disk which has replacement, first set rdev to NULL and then set replacement to rdev, finally set replacement to NULL (see raid10_remove_disk()). If io is submitted during the same time, it might read both rdev and replacement as NULL, and io will not be submitted. rdev -> NULL read rdev replacement -> NULL read replacement Fix it by reading replacement first and rdev later, meanwhile, use smp_mb() to prevent memory reordering.
Looks good, feel free to add: Reviewed-by: Yu Kuai <redacted>
quoted hunk ↗ jump to hunk
Fixes: 475b0321a4df ("md/raid10: writes should get directed to replacement as well as original.") Signed-off-by: Li Nan <redacted> --- drivers/md/raid10.c | 22 ++++++++++++++++++---- 1 file changed, 18 insertions(+), 4 deletions(-)diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c index 70cc87c7ee57..25a5a7b1e95c 100644 --- a/drivers/md/raid10.c +++ b/drivers/md/raid10.c@@ -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;@@ -1479,9 +1487,15 @@ 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)))