Re: [BUG] disk_free_ptbl_rcu_cb() crash

[Jens Axboe <jaxboe@fusionio.com>]

On 2010-10-23 23:10, Eric Dumazet wrote:
> Current Linus tree makes my machine crash in disk_free_ptbl_rcu_cb(),
> while booting...
> 
> commit 7681bfeeccff5ef seems the problem ?
> 
> Following patch solves the NULL dereference, but this is only to show
> you where the problem is, not a real fix, of course.

Darn. Your fix is on the right path, you missed one though. I think it's
cleaner to move this into the elevator helpers, so that the callers can
remain clean.

Can you verify that this works too?

diff --git a/block/elevator.c b/block/elevator.c
index 2569512..f08ae2d 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -590,11 +590,8 @@ void elv_drain_elevator(struct request_queue *q)
 /*
  * Call with queue lock held, interrupts disabled
  */
-void elv_quiesce_start(struct request_queue *q)
+void __elv_quiesce_start(struct request_queue *q)
 {
-	if (!q->elevator)
-		return;
-
 	queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
 
 	/*
@@ -610,11 +607,31 @@ void elv_quiesce_start(struct request_queue *q)
 	}
 }
 
-void elv_quiesce_end(struct request_queue *q)
+void elv_quiesce_start(struct request_queue *q)
+{
+	if (q->elevator) {
+		spin_lock_irq(q->queue_lock);
+		__elv_quiesce_start(q);
+		spin_unlock_irq(q->queue_lock);
+	}
+}
+
+void __elv_quiesce_end(struct request_queue *q)
 {
 	queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
 }
 
+void elv_quiesce_end(struct request_queue *q)
+{
+	if (q->elevator) {
+		unsigned long flags;
+
+		spin_lock_irqsave(q->queue_lock, flags);
+		__elv_quiesce_end(q);
+		spin_unlock_irqrestore(q->queue_lock, flags);
+	}
+}
+
 void elv_insert(struct request_queue *q, struct request *rq, int where)
 {
 	int unplug_it = 1;
@@ -969,7 +986,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 	 * Turn on BYPASS and drain all requests w/ elevator private data
 	 */
 	spin_lock_irq(q->queue_lock);
-	elv_quiesce_start(q);
+	__elv_quiesce_start(q);
 
 	/*
 	 * Remember old elevator.
@@ -995,9 +1012,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 	 * finally exit old elevator and turn off BYPASS.
 	 */
 	elevator_exit(old_elevator);
-	spin_lock_irq(q->queue_lock);
 	elv_quiesce_end(q);
-	spin_unlock_irq(q->queue_lock);
 
 	blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);
 
diff --git a/block/genhd.c b/block/genhd.c
index a8adf96..7d4d860 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -930,14 +930,9 @@ static void disk_free_ptbl_rcu_cb(struct rcu_head *head)
 	struct disk_part_tbl *ptbl =
 		container_of(head, struct disk_part_tbl, rcu_head);
 	struct gendisk *disk = ptbl->disk;
-	struct request_queue *q = disk->queue;
-	unsigned long flags;
 
 	kfree(ptbl);
-
-	spin_lock_irqsave(q->queue_lock, flags);
-	elv_quiesce_end(q);
-	spin_unlock_irqrestore(q->queue_lock, flags);
+	elv_quiesce_end(disk->queue);
 }
 
 /**
@@ -962,10 +957,7 @@ static void disk_replace_part_tbl(struct gendisk *disk,
 	if (old_ptbl) {
 		rcu_assign_pointer(old_ptbl->last_lookup, NULL);
 
-		spin_lock_irq(q->queue_lock);
 		elv_quiesce_start(q);
-		spin_unlock_irq(q->queue_lock);
-
 		call_rcu(&old_ptbl->rcu_head, disk_free_ptbl_rcu_cb);
 	}
 }
diff --git a/fs/partitions/check.c b/fs/partitions/check.c
index b81bfc0..cf4d1ee 100644
--- a/fs/partitions/check.c
+++ b/fs/partitions/check.c
@@ -367,16 +367,13 @@ static void delete_partition_rcu_cb(struct rcu_head *head)
 	struct hd_struct *part = container_of(head, struct hd_struct, rcu_head);
 	struct gendisk *disk = part_to_disk(part);
 	struct request_queue *q = disk->queue;
-	unsigned long flags;
 
 	part->start_sect = 0;
 	part->nr_sects = 0;
 	part_stat_set_all(part, 0);
 	put_device(part_to_dev(part));
 
-	spin_lock_irqsave(q->queue_lock, flags);
 	elv_quiesce_end(q);
-	spin_unlock_irqrestore(q->queue_lock, flags);
 }
 
 void delete_partition(struct gendisk *disk, int partno)
@@ -398,9 +395,7 @@ void delete_partition(struct gendisk *disk, int partno)
 	kobject_put(part->holder_dir);
 	device_del(part_to_dev(part));
 
-	spin_lock_irq(q->queue_lock);
 	elv_quiesce_start(q);
-	spin_unlock_irq(q->queue_lock);
 
 	call_rcu(&part->rcu_head, delete_partition_rcu_cb);
 }
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 80a0ece..2d30300 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -122,7 +122,9 @@ extern void elv_completed_request(struct request_queue *, struct request *);
 extern int elv_set_request(struct request_queue *, struct request *, gfp_t);
 extern void elv_put_request(struct request_queue *, struct request *);
 extern void elv_drain_elevator(struct request_queue *);
+extern void __elv_quiesce_start(struct request_queue *);
 extern void elv_quiesce_start(struct request_queue *);
+extern void __elv_quiesce_end(struct request_queue *);
 extern void elv_quiesce_end(struct request_queue *);
 
 /*

-- 
Jens Axboe