On Fri, 17 Aug 2018 01:38:47 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> On Thu, 16 Aug 2018 10:38:02 -0400
> Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> > 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?
>
> Ah, yes, but we need to clear "ret" in that case.
Sure.
>
> Thanks!
>
> >
> > 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) {
+ ret = 0;
> > + goto out_unlock_bdev;
+ }
-- Steve
> > if (value)
> > ret = blk_trace_setup_queue(q, bdev);
> > else
> >
> > -- Steve
>
>
