Merge tag 'block-6.19-20260102' of git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux

Pull block fixes from Jens Axboe:

 - Scan partition tables asynchronously for ublk, similarly to how nvme
   does it. This avoids potential deadlocks, which is why nvme does it
   that way too. Includes a set of selftests as well.

 - MD pull request via Yu:
     - Fix null-pointer dereference in raid5 sysfs group_thread_cnt
       store (Tuo Li)
     - Fix possible mempool corruption during raid1 raid_disks update
       via sysfs (FengWei Shih)
     - Fix logical_block_size configuration being overwritten during
       super_1_validate() (Li Nan)
     - Fix forward incompatibility with configurable logical block size:
       arrays assembled on new kernels could not be assembled on older
       kernels (v6.18 and before) due to non-zero reserved pad rejection
       (Li Nan)
     - Fix static checker warning about iterator not incremented (Li Nan)

 - Skip CPU offlining notifications on unmapped hardware queues

 - bfq-iosched block stats fix

 - Fix outdated comment in bfq-iosched

* tag 'block-6.19-20260102' of git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux:
  block, bfq: update outdated comment
  blk-mq: skip CPU offline notify on unmapped hctx
  selftests/ublk: fix Makefile to rebuild on header changes
  selftests/ublk: add test for async partition scan
  ublk: scan partition in async way
  block,bfq: fix aux stat accumulation destination
  md: Fix forward incompatibility from configurable logical block size
  md: Fix logical_block_size configuration being overwritten
  md: suspend array while updating raid_disks via sysfs
  md/raid5: fix possible null-pointer dereferences in raid5_store_group_thread_cnt()
  md: Fix static checker warning in analyze_sbs

3 files changed, 88 insertions, 18 deletions

diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 49c208457198..837fedb02e0d 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -237,6 +237,7 @@ struct ublk_device {
 	bool canceling;
 	pid_t 	ublksrv_tgid;
 	struct delayed_work	exit_work;
+	struct work_struct	partition_scan_work;
 
 	struct ublk_queue       *queues[];
 };
@@ -254,6 +255,20 @@ static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub,
 		u16 q_id, u16 tag, struct ublk_io *io, size_t offset);
 static inline unsigned int ublk_req_build_flags(struct request *req);
 
+static void ublk_partition_scan_work(struct work_struct *work)
+{
+	struct ublk_device *ub =
+		container_of(work, struct ublk_device, partition_scan_work);
+
+	if (WARN_ON_ONCE(!test_and_clear_bit(GD_SUPPRESS_PART_SCAN,
+					     &ub->ub_disk->state)))
+		return;
+
+	mutex_lock(&ub->ub_disk->open_mutex);
+	bdev_disk_changed(ub->ub_disk, false);
+	mutex_unlock(&ub->ub_disk->open_mutex);
+}
+
 static inline struct ublksrv_io_desc *
 ublk_get_iod(const struct ublk_queue *ubq, unsigned tag)
 {
@@ -2026,6 +2041,7 @@ static void ublk_stop_dev(struct ublk_device *ub)
 	mutex_lock(&ub->mutex);
 	ublk_stop_dev_unlocked(ub);
 	mutex_unlock(&ub->mutex);
+	flush_work(&ub->partition_scan_work);
 	ublk_cancel_dev(ub);
 }
 
@@ -2954,9 +2970,17 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub,
 
 	ublk_apply_params(ub);
 
-	/* don't probe partitions if any daemon task is un-trusted */
-	if (ub->unprivileged_daemons)
-		set_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
+	/*
+	 * Suppress partition scan to avoid potential IO hang.
+	 *
+	 * If ublk server error occurs during partition scan, the IO may
+	 * wait while holding ub->mutex, which can deadlock with other
+	 * operations that need the mutex. Defer partition scan to async
+	 * work.
+	 * For unprivileged daemons, keep GD_SUPPRESS_PART_SCAN set
+	 * permanently.
+	 */
+	set_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
 
 	ublk_get_device(ub);
 	ub->dev_info.state = UBLK_S_DEV_LIVE;
@@ -2973,6 +2997,10 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub,
 
 	set_bit(UB_STATE_USED, &ub->state);
 
+	/* Schedule async partition scan for trusted daemons */
+	if (!ub->unprivileged_daemons)
+		schedule_work(&ub->partition_scan_work);
+
 out_put_cdev:
 	if (ret) {
 		ublk_detach_disk(ub);
@@ -3138,6 +3166,7 @@ static int ublk_ctrl_add_dev(const struct ublksrv_ctrl_cmd *header)
 	mutex_init(&ub->mutex);
 	spin_lock_init(&ub->lock);
 	mutex_init(&ub->cancel_mutex);
+	INIT_WORK(&ub->partition_scan_work, ublk_partition_scan_work);
 
 	ret = ublk_alloc_dev_number(ub, header->dev_id);
 	if (ret < 0)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index e5922a682953..6d73f6e196a9 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1999,7 +1999,6 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *freshest, struc
 		mddev->layout = le32_to_cpu(sb->layout);
 		mddev->raid_disks = le32_to_cpu(sb->raid_disks);
 		mddev->dev_sectors = le64_to_cpu(sb->size);
-		mddev->logical_block_size = le32_to_cpu(sb->logical_block_size);
 		mddev->events = ev1;
 		mddev->bitmap_info.offset = 0;
 		mddev->bitmap_info.space = 0;
@@ -2015,6 +2014,9 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *freshest, struc
 
 		mddev->max_disks =  (4096-256)/2;
 
+		if (!mddev->logical_block_size)
+			mddev->logical_block_size = le32_to_cpu(sb->logical_block_size);
+
 		if ((le32_to_cpu(sb->feature_map) & MD_FEATURE_BITMAP_OFFSET) &&
 		    mddev->bitmap_info.file == NULL) {
 			mddev->bitmap_info.offset =
@@ -3882,7 +3884,6 @@ out_free_rdev:
 
 static int analyze_sbs(struct mddev *mddev)
 {
-	int i;
 	struct md_rdev *rdev, *freshest, *tmp;
 
 	freshest = NULL;
@@ -3909,11 +3910,9 @@ static int analyze_sbs(struct mddev *mddev)
 	super_types[mddev->major_version].
 		validate_super(mddev, NULL/*freshest*/, freshest);
 
-	i = 0;
 	rdev_for_each_safe(rdev, tmp, mddev) {
 		if (mddev->max_disks &&
-		    (rdev->desc_nr >= mddev->max_disks ||
-		     i > mddev->max_disks)) {
+		    rdev->desc_nr >= mddev->max_disks) {
 			pr_warn("md: %s: %pg: only %d devices permitted\n",
 				mdname(mddev), rdev->bdev,
 				mddev->max_disks);
@@ -4407,7 +4406,7 @@ 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 +4431,7 @@ 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 =
@@ -5981,13 +5980,33 @@ lbs_store(struct mddev *mddev, const char *buf, size_t len)
 	if (mddev->major_version == 0)
 		return -EINVAL;
 
-	if (mddev->pers)
-		return -EBUSY;
-
 	err = kstrtouint(buf, 10, &lbs);
 	if (err < 0)
 		return -EINVAL;
 
+	if (mddev->pers) {
+		unsigned int curr_lbs;
+
+		if (mddev->logical_block_size)
+			return -EBUSY;
+		/*
+		 * To fix forward compatibility issues, LBS is not
+		 * configured for arrays from old kernels (<=6.18) by default.
+		 * If the user confirms no rollback to old kernels,
+		 * enable LBS by writing current LBS — to prevent data
+		 * loss from LBS changes.
+		 */
+		curr_lbs = queue_logical_block_size(mddev->gendisk->queue);
+		if (lbs != curr_lbs)
+			return -EINVAL;
+
+		mddev->logical_block_size = curr_lbs;
+		set_bit(MD_SB_CHANGE_DEVS, &mddev->sb_flags);
+		pr_info("%s: logical block size configured successfully, array will not be assembled in old kernels (<= 6.18)\n",
+			mdname(mddev));
+		return len;
+	}
+
 	err = mddev_lock(mddev);
 	if (err)
 		goto unlock;
@@ -6163,7 +6182,27 @@ int mddev_stack_rdev_limits(struct mddev *mddev, struct queue_limits *lim,
 			mdname(mddev));
 		return -EINVAL;
 	}
-	mddev->logical_block_size = lim->logical_block_size;
+
+	/* Only 1.x meta needs to set logical block size */
+	if (mddev->major_version == 0)
+		return 0;
+
+	/*
+	 * Fix forward compatibility issue. Only set LBS by default for
+	 * new arrays, mddev->events == 0 indicates the array was just
+	 * created. When assembling an array, read LBS from the superblock
+	 * instead — LBS is 0 in superblocks created by old kernels.
+	 */
+	if (!mddev->events) {
+		pr_info("%s: array will not be assembled in old kernels that lack configurable LBS support (<= 6.18)\n",
+			mdname(mddev));
+		mddev->logical_block_size = lim->logical_block_size;
+	}
+
+	if (!mddev->logical_block_size)
+		pr_warn("%s: echo current LBS to md/logical_block_size to prevent data loss issues from LBS changes.\n"
+			"\tNote: After setting, array will not be assembled in old kernels (<= 6.18)\n",
+			mdname(mddev));
 
 	return 0;
 }
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index e57ce3295292..8dc98f545969 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7187,12 +7187,14 @@ raid5_store_group_thread_cnt(struct mddev *mddev, const char *page, size_t len)
 	err = mddev_suspend_and_lock(mddev);
 	if (err)
 		return err;
+	conf = mddev->private;
+	if (!conf) {
+		mddev_unlock_and_resume(mddev);
+		return -ENODEV;
+	}
 	raid5_quiesce(mddev, true);
 
-	conf = mddev->private;
-	if (!conf)
-		err = -ENODEV;
-	else if (new != conf->worker_cnt_per_group) {
+	if (new != conf->worker_cnt_per_group) {
 		old_groups = conf->worker_groups;
 		if (old_groups)
 			flush_workqueue(raid5_wq);