On Thu, 16 Aug 2018 18:51:15 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> 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@xxxxxxxxxx>
> Cc: Jens Axboe <axboe@xxxxxxxxx>
> Cc: linux-block@xxxxxxxxxxxxxxx
> ---
> 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;
Hmm, why not just do this? Does this fix it too?
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 987d9a9ae283..10b2b9c5fd25 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -1841,6 +1841,8 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
mutex_lock(&q->blk_trace_mutex);
if (attr == &dev_attr_enable) {
+ if (!!value == !!q->blk_trace)
+ goto out_unlock_bdev;
if (value)
ret = blk_trace_setup_queue(q, bdev);
else
-- Steve
