blktrace: don't increase blk_probes_ref if failed to setup blk trace

do_blk_trace_setup() may return EBUSY, but the current code
doesn't decrease blk_probes_ref in this case.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <49C2F5FF.80002@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 3 insertions, 3 deletions

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 223b92e77b3f..11e7c8d9d222 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -468,9 +468,6 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
         bt->pid = buts->pid;
         bt->trace_state = Blktrace_setup;
 
-        if (atomic_add_return(1, &blk_probes_ref) == 1)
-                blk_register_tracepoints();
-
         ret = -EBUSY;
         old_bt = xchg(&q->blk_trace, bt);
         if (old_bt) {
@@ -478,6 +475,9 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
                 goto err;
         }
 
+        if (atomic_add_return(1, &blk_probes_ref) == 1)
+                blk_register_tracepoints();
+
         return 0;
 err:
         if (bt) {