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Subject[PATCH 2/2] tracing/blktrace: Fix to allow setting same value
Date
Current trace-enable attribute in sysfs returns an error
if user writes the same setting value as current one,
e.g.

# cat /sys/block/sda/trace/enable
0
# echo 0 > /sys/block/sda/trace/enable
bash: echo: write error: Invalid argument
# echo 1 > /sys/block/sda/trace/enable
# echo 1 > /sys/block/sda/trace/enable
bash: echo: write error: Device or resource busy

But this is not a preferred behavior, it should ignore
if new setting is same as current one. This fixes the
problem as below.

# cat /sys/block/sda/trace/enable
0
# echo 0 > /sys/block/sda/trace/enable
# echo 1 > /sys/block/sda/trace/enable
# echo 1 > /sys/block/sda/trace/enable

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org
---
kernel/trace/blktrace.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 987d9a9ae283..e67db1e8a000 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -1602,11 +1602,11 @@ static int blk_trace_remove_queue(struct request_queue *q)
struct blk_trace *bt;

bt = xchg(&q->blk_trace, NULL);
- if (bt == NULL)
- return -EINVAL;
+ if (bt != NULL) {
+ put_probe_ref();
+ blk_trace_free(bt);
+ }

- put_probe_ref();
- blk_trace_free(bt);
return 0;
}

@@ -1619,6 +1619,9 @@ static int blk_trace_setup_queue(struct request_queue *q,
struct blk_trace *bt = NULL;
int ret = -ENOMEM;

+ if (q->blk_trace)
+ return 0;
+
bt = kzalloc(sizeof(*bt), GFP_KERNEL);
if (!bt)
return -ENOMEM;
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