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

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Message-ID: <20190116171259.GB10164@kroah.com>
Date:   Wed, 16 Jan 2019 18:12:59 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.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, Jan 16, 2019 at 09:38:09AM -0700, Mathieu Poirier wrote:
> 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.

But is the driver able to be unloaded?  Unbound from the device manually
through sysfs?  There's lots of ways devices are "removed" that don't
involved physical removal :)

thanks,

greg k-h