Commit c3dbe541 authored by Jan Kara's avatar Jan Kara Committed by Jens Axboe
Browse files

blktrace: Avoid sparse warnings when assigning q->blk_trace 



Mostly for historical reasons, q->blk_trace is assigned through xchg()
and cmpxchg() atomic operations. Although this is correct, sparse
complains about this because it violates rcu annotations since commit
c780e86d ("blktrace: Protect q->blk_trace with RCU") which started
to use rcu for accessing q->blk_trace. Furthermore there's no real need
for atomic operations anymore since all changes to q->blk_trace happen
under q->blk_trace_mutex and since it also makes more sense to check if
q->blk_trace is set with the mutex held earlier.

So let's just replace xchg() with rcu_replace_pointer() and cmpxchg()
with explicit check and rcu_assign_pointer(). This makes the code more
efficient and sparse happy.

Reported-by: default avatarkbuild test robot <lkp@intel.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 1b0b2836

kernel/trace/blktrace.c

+8 −11
Original line number Diff line number Diff line
@@ -347,7 +347,8 @@ static int __blk_trace_remove(struct request_queue *q) 
{

	struct blk_trace *bt;



	bt = xchg(&q->blk_trace, NULL);

	bt = rcu_replace_pointer(q->blk_trace, NULL,

				 lockdep_is_held(&q->blk_trace_mutex));

	if (!bt)

		return -EINVAL;
@@ -501,7 +502,8 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev, 
	 * bdev can be NULL, as with scsi-generic, this is a helpful as

	 * we can be.

	 */

	if (q->blk_trace) {

	if (rcu_dereference_protected(q->blk_trace,

				      lockdep_is_held(&q->blk_trace_mutex))) {

		pr_warn("Concurrent blktraces are not allowed on %s\n",

			buts->name);

		return -EBUSY;
@@ -556,10 +558,7 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev, 
	bt->pid = buts->pid;

	bt->trace_state = Blktrace_setup;



	ret = -EBUSY;

	if (cmpxchg(&q->blk_trace, NULL, bt))

		goto err;



	rcu_assign_pointer(q->blk_trace, bt);

	get_probe_ref();



	ret = 0;
@@ -1642,7 +1641,8 @@ static int blk_trace_remove_queue(struct request_queue *q) 
{

	struct blk_trace *bt;



	bt = xchg(&q->blk_trace, NULL);

	bt = rcu_replace_pointer(q->blk_trace, NULL,

				 lockdep_is_held(&q->blk_trace_mutex));

	if (bt == NULL)

		return -EINVAL;
@@ -1674,10 +1674,7 @@ static int blk_trace_setup_queue(struct request_queue *q, 


	blk_trace_setup_lba(bt, bdev);



	ret = -EBUSY;

	if (cmpxchg(&q->blk_trace, NULL, bt))

		goto free_bt;



	rcu_assign_pointer(q->blk_trace, bt);

	get_probe_ref();

	return 0;

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