block: prevent adding/deleting disk during updating nr_hw_queues

Both adding/deleting disk code are reader of `nr_hw_queues`, so we can't
allow them in-progress when updating nr_hw_queues, kernel panic and
kasan has been reported in [1].

Prevent adding/deleting disk during updating nr_hw_queues by adding
rw_semaphore to tagset, write lock is grabbed in blk_mq_update_nr_hw_queues(),
and read lock is acquired when adding/deleting disk.

Also mark GFP_NOIO allocation scope for adding/deleting disk because
blk_mq_update_nr_hw_queues() is part of some driver's error handler.

This way avoids lot of trouble.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Suggested-by: Nilay Shroff <nilay@linux.ibm.com>
Reported-by: Nilay Shroff <nilay@linux.ibm.com>
Closes: https://lore.kernel.org/linux-block/a5896cdb-a59a-4a37-9f99-20522f5d2987@linux.ibm.com/
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250505141805.2751237-9-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -4846,6 +4846,8 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
 			goto out_free_srcu;
 	}
 
+	init_rwsem(&set->update_nr_hwq_lock);
+
 	ret = -ENOMEM;
 	set->tags = kcalloc_node(set->nr_hw_queues,
 				 sizeof(struct blk_mq_tags *), GFP_KERNEL,
@@ -5141,9 +5143,11 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
 
 void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)
 {
+	down_write(&set->update_nr_hwq_lock);
 	mutex_lock(&set->tag_list_lock);
 	__blk_mq_update_nr_hw_queues(set, nr_hw_queues);
 	mutex_unlock(&set->tag_list_lock);
+	up_write(&set->update_nr_hwq_lock);
 }
 EXPORT_SYMBOL_GPL(blk_mq_update_nr_hw_queues);
 

block/genhd.c

@@ -415,17 +415,7 @@ static void add_disk_final(struct gendisk *disk)
 	set_bit(GD_ADDED, &disk->state);
 }
 
-/**
+static int __add_disk(struct device *parent, struct gendisk *disk,
- * add_disk_fwnode - add disk information to kernel list with fwnode
- * @parent: parent device for the disk
- * @disk: per-device partitioning information
- * @groups: Additional per-device sysfs groups
- * @fwnode: attached disk fwnode
- *
- * This function registers the partitioning information in @disk
- * with the kernel. Also attach a fwnode to the disk device.
- */
-int __must_check add_disk_fwnode(struct device *parent, struct gendisk *disk,
 		      const struct attribute_group **groups,
 		      struct fwnode_handle *fwnode)
 
@@ -550,7 +540,6 @@ int __must_check add_disk_fwnode(struct device *parent, struct gendisk *disk,
 		 */
 		disk->part0->bd_dev = MKDEV(disk->major, disk->first_minor);
 	}
-	add_disk_final(disk);
 	return 0;
 
 out_unregister_bdi:
@@ -580,6 +569,45 @@ int __must_check add_disk_fwnode(struct device *parent, struct gendisk *disk,
 	}
 	return ret;
 }
+
+/**
+ * add_disk_fwnode - add disk information to kernel list with fwnode
+ * @parent: parent device for the disk
+ * @disk: per-device partitioning information
+ * @groups: Additional per-device sysfs groups
+ * @fwnode: attached disk fwnode
+ *
+ * This function registers the partitioning information in @disk
+ * with the kernel. Also attach a fwnode to the disk device.
+ */
+int __must_check add_disk_fwnode(struct device *parent, struct gendisk *disk,
+				 const struct attribute_group **groups,
+				 struct fwnode_handle *fwnode)
+{
+	struct blk_mq_tag_set *set;
+	unsigned int memflags;
+	int ret;
+
+	if (queue_is_mq(disk->queue)) {
+		set = disk->queue->tag_set;
+		memflags = memalloc_noio_save();
+		down_read(&set->update_nr_hwq_lock);
+		ret = __add_disk(parent, disk, groups, fwnode);
+		up_read(&set->update_nr_hwq_lock);
+		memalloc_noio_restore(memflags);
+	} else {
+		ret = __add_disk(parent, disk, groups, fwnode);
+	}
+
+	/*
+	 * add_disk_final() needn't to read `nr_hw_queues`, so move it out
+	 * of read lock `set->update_nr_hwq_lock` for avoiding unnecessary
+	 * lock dependency on `disk->open_mutex` from scanning partition.
+	 */
+	if (!ret)
+		add_disk_final(disk);
+	return ret;
+}
 EXPORT_SYMBOL_GPL(add_disk_fwnode);
 
 /**
@@ -660,26 +688,7 @@ void blk_mark_disk_dead(struct gendisk *disk)
 }
 EXPORT_SYMBOL_GPL(blk_mark_disk_dead);
 
-/**
+static void __del_gendisk(struct gendisk *disk)
- * del_gendisk - remove the gendisk
- * @disk: the struct gendisk to remove
- *
- * Removes the gendisk and all its associated resources. This deletes the
- * partitions associated with the gendisk, and unregisters the associated
- * request_queue.
- *
- * This is the counter to the respective __device_add_disk() call.
- *
- * The final removal of the struct gendisk happens when its refcount reaches 0
- * with put_disk(), which should be called after del_gendisk(), if
- * __device_add_disk() was used.
- *
- * Drivers exist which depend on the release of the gendisk to be synchronous,
- * it should not be deferred.
- *
- * Context: can sleep
- */
-void del_gendisk(struct gendisk *disk)
 {
 	struct request_queue *q = disk->queue;
 	struct block_device *part;
@@ -772,6 +781,42 @@ void del_gendisk(struct gendisk *disk)
 	if (start_drain)
 		blk_unfreeze_release_lock(q);
 }
+
+/**
+ * del_gendisk - remove the gendisk
+ * @disk: the struct gendisk to remove
+ *
+ * Removes the gendisk and all its associated resources. This deletes the
+ * partitions associated with the gendisk, and unregisters the associated
+ * request_queue.
+ *
+ * This is the counter to the respective __device_add_disk() call.
+ *
+ * The final removal of the struct gendisk happens when its refcount reaches 0
+ * with put_disk(), which should be called after del_gendisk(), if
+ * __device_add_disk() was used.
+ *
+ * Drivers exist which depend on the release of the gendisk to be synchronous,
+ * it should not be deferred.
+ *
+ * Context: can sleep
+ */
+void del_gendisk(struct gendisk *disk)
+{
+	struct blk_mq_tag_set *set;
+	unsigned int memflags;
+
+	if (!queue_is_mq(disk->queue)) {
+		__del_gendisk(disk);
+	} else {
+		set = disk->queue->tag_set;
+		memflags = memalloc_noio_save();
+		down_read(&set->update_nr_hwq_lock);
+		__del_gendisk(disk);
+		up_read(&set->update_nr_hwq_lock);
+		memalloc_noio_restore(memflags);
+	}
+}
 EXPORT_SYMBOL(del_gendisk);
 
 /**

include/linux/blk-mq.h

@@ -9,6 +9,7 @@
 #include <linux/prefetch.h>
 #include <linux/srcu.h>
 #include <linux/rw_hint.h>
+#include <linux/rwsem.h>
 
 struct blk_mq_tags;
 struct blk_flush_queue;
@@ -527,6 +528,8 @@ struct blk_mq_tag_set {
 	struct mutex		tag_list_lock;
 	struct list_head	tag_list;
 	struct srcu_struct	*srcu;
+
+	struct rw_semaphore	update_nr_hwq_lock;
 };
 
 /**