Forwarded: [PATCH] BUG: sleeping function called from invalid context in null_insert_page

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Subject: [PATCH] BUG: sleeping function called from invalid context in null_insert_page
Author: jchuang26@xxxxxxxxxxxxxx

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Reported-by: syzbot+95fdab36405e5ffdb680@xxxxxxxxxxxxxxxxxxxxxxxxx

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 6beb1f5b7..7f3fbac0f 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -70,6 +70,7 @@ static DEFINE_MUTEX(lock);
 static int null_major;
 static DEFINE_IDA(nullb_indexes);
 static struct blk_mq_tag_set tag_set;
+static struct blk_mq_tag_set blocking_tag_set;
 
 enum {
 	NULL_IRQ_NONE		= 0,
@@ -1847,34 +1848,44 @@ static int null_init_tag_set(struct blk_mq_tag_set *set, int poll_queues)
 	return blk_mq_alloc_tag_set(set);
 }
 
-static int null_init_global_tag_set(void)
+static int null_init_global_tag_set(struct blk_mq_tag_set *set, bool blocking)
 {
 	int error;
 
-	if (tag_set.ops)
+	if (set->ops)
 		return 0;
 
-	tag_set.nr_hw_queues = g_submit_queues;
-	tag_set.queue_depth = g_hw_queue_depth;
-	tag_set.numa_node = g_home_node;
+	set->nr_hw_queues = g_submit_queues;
+	set->queue_depth = g_hw_queue_depth;
+	set->numa_node = g_home_node;
 	if (g_no_sched)
-		tag_set.flags |= BLK_MQ_F_NO_SCHED_BY_DEFAULT;
+		set->flags |= BLK_MQ_F_NO_SCHED_BY_DEFAULT;
 	if (g_shared_tag_bitmap)
-		tag_set.flags |= BLK_MQ_F_TAG_HCTX_SHARED;
-	if (g_blocking)
-		tag_set.flags |= BLK_MQ_F_BLOCKING;
+		set->flags |= BLK_MQ_F_TAG_HCTX_SHARED;
+	if (blocking)
+		set->flags |= BLK_MQ_F_BLOCKING;
 
-	error = null_init_tag_set(&tag_set, g_poll_queues);
+	error = null_init_tag_set(set, g_poll_queues);
 	if (error)
-		tag_set.ops = NULL;
+		set->ops = NULL;
 	return error;
 }
 
 static int null_setup_tagset(struct nullb *nullb)
 {
 	if (nullb->dev->shared_tags) {
-		nullb->tag_set = &tag_set;
-		return null_init_global_tag_set();
+		bool blocking = g_blocking || nullb->dev->blocking;
+
+		/*
+		 * Some memory-backed devices can sleep in their request
+		 * submission path, which is invalid if the tag set is
+		 * non-blocking since the block layer then calls the driver
+		 * under rcu_read_lock(). The blocking flag is fixed when a tag
+		 * set is allocated, so use a dedicated blocking global tag set
+		 * for such devices.
+		 */
+		nullb->tag_set = blocking ? &blocking_tag_set : &tag_set;
+		return null_init_global_tag_set(nullb->tag_set, blocking);
 	}
 
 	nullb->tag_set = &nullb->__tag_set;
@@ -2195,6 +2206,8 @@ static int __init null_init(void)
 	unregister_blkdev(null_major, "nullb");
 	if (tag_set.ops)
 		blk_mq_free_tag_set(&tag_set);
+	if (blocking_tag_set.ops)
+		blk_mq_free_tag_set(&blocking_tag_set);
 	return ret;
 }
 
@@ -2215,6 +2228,8 @@ static void __exit null_exit(void)
 
 	if (tag_set.ops)
 		blk_mq_free_tag_set(&tag_set);
+	if (blocking_tag_set.ops)
+		blk_mq_free_tag_set(&blocking_tag_set);
 }
 
 module_init(null_init);