linux-kernel - Re: [PATCH 2/7] coresight: perf: Add "sinks" group to PMU directory

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Message-ID: <CANLsYkw_=_OC-95HRMxTZfpAe4UzAuidPJcZmL_T-LbkOwWCkQ@mail.gmail.com>
Date:   Wed, 16 Jan 2019 09:38:09 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>, ast@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        "Suzuki K. Poulose" <suzuki.poulose@....com>,
        linux-s390@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/7] coresight: perf: Add "sinks" group to PMU directory

On Wed, 16 Jan 2019 at 09:33, Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Wed, Jan 16, 2019 at 09:14:33AM -0700, Mathieu Poirier wrote:
> > On Wed, 16 Jan 2019 at 08:39, Greg KH <gregkh@...uxfoundation.org> wrote:
> > >
> > > On Tue, Jan 15, 2019 at 04:07:37PM -0700, Mathieu Poirier wrote:
> > > > Add a "sinks" directory entry so that users can see all the sinks
> > > > available in the system in a single place.  Individual sink are added
> > > > as they are registered with the coresight bus.
> > > >
> > > > Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> > > > ---
> > > >  .../hwtracing/coresight/coresight-etm-perf.c  | 43 +++++++++++++++++++
> > > >  .../hwtracing/coresight/coresight-etm-perf.h  |  1 +
> > > >  drivers/hwtracing/coresight/coresight.c       | 17 ++++++++
> > > >  3 files changed, 61 insertions(+)
> > > >
> > > > diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> > > > index f21eb28b6782..292bd409a68c 100644
> > > > --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> > > > +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> > > > @@ -14,6 +14,7 @@
> > > >  #include <linux/perf_event.h>
> > > >  #include <linux/percpu-defs.h>
> > > >  #include <linux/slab.h>
> > > > +#include <linux/stringhash.h>
> > > >  #include <linux/types.h>
> > > >  #include <linux/workqueue.h>
> > > >
> > > > @@ -43,8 +44,18 @@ static const struct attribute_group etm_pmu_format_group = {
> > > >       .attrs  = etm_config_formats_attr,
> > > >  };
> > > >
> > > > +static struct attribute *etm_config_sinks_attr[] = {
> > > > +     NULL,
> > > > +};
> > > > +
> > > > +static const struct attribute_group etm_pmu_sinks_group = {
> > > > +     .name   = "sinks",
> > > > +     .attrs  = etm_config_sinks_attr,
> > > > +};
> > > > +
> > > >  static const struct attribute_group *etm_pmu_attr_groups[] = {
> > > >       &etm_pmu_format_group,
> > > > +     &etm_pmu_sinks_group,
> > > >       NULL,
> > > >  };
> > > >
> > > > @@ -479,6 +490,38 @@ int etm_perf_symlink(struct coresight_device *csdev, bool link)
> > > >       return 0;
> > > >  }
> > > >
> > > > +static ssize_t etm_perf_sink_name_show(struct device *dev,
> > > > +                                    struct device_attribute *dattr,
> > > > +                                    char *buf)
> > > > +{
> > > > +     /* See function coresight_sink_by_id() to know where this is used */
> > > > +     u32 hash = hashlen_hash(hashlen_string(NULL, dattr->attr.name));
> > > > +
> > > > +     return scnprintf(buf, PAGE_SIZE, "%x\n", hash);
> > > > +}
> > > > +
> > > > +int etm_perf_symlink_sink(struct coresight_device *csdev)
> > > > +{
> > > > +     struct device *pmu_dev = etm_pmu.dev;
> > > > +     struct device *pdev = csdev->dev.parent;
> > > > +     struct device_attribute *dev_attr;
> > > > +
> > > > +     if (csdev->type != CORESIGHT_DEV_TYPE_SINK &&
> > > > +         csdev->type != CORESIGHT_DEV_TYPE_LINKSINK)
> > > > +             return -EINVAL;
> > > > +
> > > > +     if (!etm_perf_up)
> > > > +             return -EPROBE_DEFER;
> > > > +
> > > > +     dev_attr = kzalloc(sizeof(*dev_attr), GFP_KERNEL);
> > > > +     dev_attr->attr.name = kstrdup(dev_name(pdev), GFP_KERNEL);
> > > > +     dev_attr->attr.mode = 0444;
> > > > +     dev_attr->show = etm_perf_sink_name_show;
> > > > +
> > > > +     return sysfs_add_file_to_group(&pmu_dev->kobj,
> > > > +                                    &dev_attr->attr, "sinks");
> > >
> > > What is so odd about this call that you needed me to review this?
> >
> > As far as I can tell nobody is feeding a dynamic struct attribute to
> > the function and I wasn't sure if it was because they were told not to
> > or simply because it wasn't needed, hence asking for a second opinion.
>
> Ah.  Well, again, this is a good question to answer:
>
> > > And what happens if this call fails, do you leak memory?

That's something I will fix in the next revision.

>
> And also, what happens when you unload the device, who frees the
> attribute's memory?

If configured, coresight devices aren't removable.

Thanks for the review,
Mathieu

>
> thanks,
>
> greg k-h