md: allow removing faulty rdev during resync

JIRA: https://issues.redhat.com/browse/RHEL-106845

commit c0ffeb6
Author: Zheng Qixing <zhengqixing@huawei.com>
Date:   Mon Jul 7 15:54:12 2025 +0800

    md: allow removing faulty rdev during resync

    During RAID resync, faulty rdev cannot be removed and will result in
    "Device or resource busy" error when attempting hot removal.

    Reproduction steps:
      mdadm -Cv /dev/md0 -l1 -n3 -e1.2 /dev/sd{b..d}
      mdadm /dev/md0 -f /dev/sdb
      mdadm /dev/md0 -r /dev/sdb
      -> mdadm: hot remove failed for /dev/sdb: Device or resource busy

    After commit 4b10a3b ("md: ensure resync is prioritized over
    recovery"), when a device becomes faulty during resync, the
    md_choose_sync_action() function returns early without calling
    remove_and_add_spares(), preventing faulty device removal.

    This patch extracts a helper function remove_spares() to support
    removing faulty devices during RAID resync operations.

    Fixes: 4b10a3b ("md: ensure resync is prioritized over recovery")
    Signed-off-by: Zheng Qixing <zhengqixing@huawei.com>
    Reviewed-by: Li Nan <linan122@huawei.com>
    Link: https://lore.kernel.org/linux-raid/20250707075412.150301-1-zhengqixing@huaweicloud.com
    Signed-off-by: Yu Kuai <yukuai3@huawei.com>

Signed-off-by: Ming Lei <ming.lei@redhat.com>

Author: Ming Lei

drivers/md/md.c

@@ -9454,17 +9454,11 @@ static bool md_spares_need_change(struct mddev *mddev)
 	return false;
 }
 
-static int remove_and_add_spares(struct mddev *mddev,
-				 struct md_rdev *this)
+static int remove_spares(struct mddev *mddev, struct md_rdev *this)
 {
 	struct md_rdev *rdev;
-	int spares = 0;
 	int removed = 0;
 
-	if (this && test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
-		/* Mustn't remove devices when resync thread is running */
-		return 0;
-
 	rdev_for_each(rdev, mddev) {
 		if ((this == NULL || rdev == this) && rdev_removeable(rdev) &&
 		    !mddev->pers->hot_remove_disk(mddev, rdev)) {
@@ -9478,6 +9472,21 @@ static int remove_and_add_spares(struct mddev *mddev,
 	if (removed && mddev->kobj.sd)
 		sysfs_notify_dirent_safe(mddev->sysfs_degraded);
 
+	return removed;
+}
+
+static int remove_and_add_spares(struct mddev *mddev,
+				 struct md_rdev *this)
+{
+	struct md_rdev *rdev;
+	int spares = 0;
+	int removed = 0;
+
+	if (this && test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
+		/* Mustn't remove devices when resync thread is running */
+		return 0;
+
+	removed = remove_spares(mddev, this);
 	if (this && removed)
 		goto no_add;
 
@@ -9520,6 +9529,7 @@ static bool md_choose_sync_action(struct mddev *mddev, int *spares)
 
 	/* Check if resync is in progress. */
 	if (mddev->recovery_cp < MaxSector) {
+		remove_spares(mddev, NULL);
 		set_bit(MD_RECOVERY_SYNC, &mddev->recovery);
 		clear_bit(MD_RECOVERY_RECOVER, &mddev->recovery);
 		return true;