diff options
| author |   Jan Kara <jack@suse.cz> | 2020-06-05 16:58:37 +0200 |
|---|---|---|
| committer |   Jens Axboe <axboe@kernel.dk> | 2020-06-17 09:07:11 -0600 |
| commit | c3dbe541ef77754729de5e82be2d6e5d267c6c8c (patch) | |
| tree | 6e0b3e4b26c3ccbbd9300ec69883b95d99400fcf /kernel | |
| parent | blktrace: break out of blktrace setup on concurrent calls (diff) | |
| download | linux-dev-c3dbe541ef77754729de5e82be2d6e5d267c6c8c.tar.xz linux-dev-c3dbe541ef77754729de5e82be2d6e5d267c6c8c.zip | |
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
c780e86dd48e ("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: kbuild test robot <lkp@intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/trace/blktrace.c | 19 |
1 files changed, 8 insertions, 11 deletions
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c index 8fd36e827f14..5ef0484513ec 100644 --- a/kernel/trace/blktrace.c +++ b/kernel/trace/blktrace.c @@ -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; |