linux-kernel - [PATCH v2] md: suspend array while updating raid

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Message-Id: <20251226101816.4506-1-dannyshih@synology.com>
Date: Fri, 26 Dec 2025 18:18:16 +0800
From: dannyshih <dannyshih@...ology.com>
To: song@...nel.org,
	yukuai@...as.com
Cc: linux-raid@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	dannyshih@...ology.com
Subject: [PATCH v2] md: suspend array while updating raid_disks via sysfs

From: FengWei Shih <dannyshih@...ology.com>

In raid1_reshape(), freeze_array() is called before modifying the r1bio
memory pool (conf->r1bio_pool) and conf->raid_disks, and
unfreeze_array() is called after the update is completed.

However, freeze_array() only waits until nr_sync_pending and
(nr_pending - nr_queued) of all buckets reaches zero. When an I/O error
occurs, nr_queued is increased and the corresponding r1bio is queued to
either retry_list or bio_end_io_list. As a result, freeze_array() may
unblock before these r1bios are released.

This can lead to a situation where conf->raid_disks and the mempool have
already been updated while queued r1bios, allocated with the old
raid_disks value, are later released. Consequently, free_r1bio() may
access memory out of bounds in put_all_bios() and release r1bios of the
wrong size to the new mempool, potentially causing issues with the
mempool as well.

Since only normal I/O might increase nr_queued while an I/O error occurs,
suspending the array avoids this issue.

Note: Updating raid_disks via ioctl SET_ARRAY_INFO already suspends
the array. Therefore, we suspend the array when updating raid_disks
via sysfs to avoid this issue too.

Signed-off-by: FengWei Shih <dannyshih@...ology.com>
---
v2:
  * Suspend array unconditionally when updating raid_disks
  * Refine commit message to describe the issue more concretely
---
 drivers/md/md.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index e5922a682953..6bcbe1c7483c 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4407,7 +4407,7 @@ raid_disks_store(struct mddev *mddev, const char *buf, size_t len)
 	if (err < 0)
 		return err;

-	err = mddev_lock(mddev);
+	err = mddev_suspend_and_lock(mddev);
 	if (err)
 		return err;
 	if (mddev->pers)
@@ -4432,7 +4432,7 @@ raid_disks_store(struct mddev *mddev, const char *buf, size_t len)
 	} else
 		mddev->raid_disks = n;
 out_unlock:
-	mddev_unlock(mddev);
+	mddev_unlock_and_resume(mddev);
 	return err ? err : len;
 }
 static struct md_sysfs_entry md_raid_disks =
-- 
2.17.1

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