blktrace: report EBUSY correctly

blk_trace_remove_queue() returns EINVAL if q->blk_trace == NULL,
but blk_trace_setup_queue() doesn't return EBUSY if
q->blk_trace != NULL.

 # echo 0 > sdaX/trace/enable
 # echo 0 > sdaX/trace/enable
 bash: echo: write error: Invalid argument
 # echo 1 > sdaX/trace/enable
 # echo 1 > sdaX/trace/enable
 (should return EBUSY)

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <49C2F614.2010101@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 3 insertions, 6 deletions

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 11e7c8d9d222..14986afdbc1c 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -1260,12 +1260,10 @@ static int blk_trace_remove_queue(struct request_queue *q)
 static int blk_trace_setup_queue(struct request_queue *q, dev_t dev)
 {
         struct blk_trace *old_bt, *bt = NULL;
-        int ret;
 
-        ret = -ENOMEM;
         bt = kzalloc(sizeof(*bt), GFP_KERNEL);
         if (!bt)
-                goto err;
+                return -ENOMEM;
 
         bt->dev = dev;
         bt->act_mask = (u16)-1;
@@ -1276,11 +1274,10 @@ static int blk_trace_setup_queue(struct request_queue *q, dev_t dev)
         if (old_bt != NULL) {
                 (void)xchg(&q->blk_trace, old_bt);
                 kfree(bt);
-                ret = -EBUSY;
+                return -EBUSY;
         }
+
         return 0;
-err:
-        return ret;
 }
 
 /*