From c3dbe541ef77754729de5e82be2d6e5d267c6c8c Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Fri, 5 Jun 2020 16:58:37 +0200
Subject: [PATCH] blktrace: Avoid sparse warnings when assigning q->blk_trace
Git-commit: c3dbe541ef77754729de5e82be2d6e5d267c6c8c
Patch-mainline: v5.8-rc2
References: bsc#1171295
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>
Signed-off-by: Luis Chamberlain <mcgrof@suse.com>
---
kernel/trace/blktrace.c | 19 ++++++++-----------
1 file 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;
--
2.27.0