linux-kernel - Re: [PATCH v2 2/7] perf/core: Use ioctl to communicate driver configuration to kernel

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Date:   Mon, 9 Jul 2018 10:49:02 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Kim Phillips <kim.phillips@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-s390@...r.kernel.org,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Will Deacon <will.deacon@....com>,
        "H. Peter Anvin" <hpa@...or.com>, heiko.carstens@...ibm.com,
        Adrian Hunter <adrian.hunter@...el.com>, ast@...nel.org,
        Ingo Molnar <mingo@...hat.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Greg KH <gregkh@...uxfoundation.org>, schwidefsky@...ibm.com,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jiri Olsa <jolsa@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/7] perf/core: Use ioctl to communicate driver
 configuration to kernel

On Fri, 6 Jul 2018 at 17:22, Kim Phillips <kim.phillips@....com> wrote:
>
> On Thu,  5 Jul 2018 16:13:42 -0600
> Mathieu Poirier <mathieu.poirier@...aro.org> wrote:
>
> Hi Mathieu,
>
> > This patch adds the mechanic needed for user space to send PMU specific
>                       ^^^^^^^^
> I think you meant 'mechanism' here:  mechanics fix cars :)

I really meant "mechanic", as in "functional details or procedure" [1]

[1]. https://www.merriam-webster.com/dictionary/mechanics

>
> > +static void perf_drv_config_replace(struct perf_event *event, void *drv_data)
> > +{
> > +     unsigned long flags;
> > +     void *old_drv_data;
> > +     struct pmu_drv_config *drv_config = &event->hw.drv_config;
> > +
> > +     if (!has_drv_config(event))
> > +             return;
> > +
> > +     /* Children take their configuration from their parent */
> > +     if (event->parent)
> > +             return;
> > +
> > +     /* Make sure the PMU doesn't get a handle on the data */
> > +     raw_spin_lock_irqsave(&drv_config->lock, flags);
> > +
> > +     old_drv_data = drv_config->config;
> > +     drv_config->config = drv_data;
> > +
> > +     raw_spin_unlock_irqrestore(&drv_config->lock, flags);
> > +
> > +     /* Free PMU private data allocated by pmu::drv_config_validate() */
> > +     event->pmu->drv_config_free(old_drv_data);
> > +}
>
> I got this stacktrace whilst testing a perf tool *without* this series
> applied, running on a kernel *with* this series applied:

That shouldn't matter as I kept the changes backward compatible
specifically to handle this situation.

>
> [  132.942054] INFO: trying to register non-static key.
> [  132.946964] the code is fine but needs lockdep annotation.
> [  132.952389] turning off the locking correctness validator.
> [  132.957818] CPU: 2 PID: 2835 Comm: perf64-sans Not tainted 4.18.0-rc3-00196-g5b5d957532a8-dirty #146
> [  132.966856] Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Jan 23 2017
> [  132.977527] Call trace:
> [  132.979947]  dump_backtrace+0x0/0x1c0
> [  132.983567]  show_stack+0x24/0x30
> [  132.986845]  dump_stack+0x90/0xb4
> [  132.990122]  register_lock_class+0x57c/0x580
> [  132.994343]  __lock_acquire.isra.12+0x6c/0x980
> [  132.998736]  lock_acquire+0x100/0x1e8
> [  133.002357]  _raw_spin_lock_irqsave+0x58/0x78
> [  133.006667]  perf_drv_config_replace+0x4c/0x80
> [  133.011061]  _free_event+0xbc/0x460
> [  133.014507]  put_event+0x2c/0x38
> [  133.017697]  perf_event_release_kernel+0x1ac/0x300
> [  133.022434]  perf_release+0x10/0x20
> [  133.025883]  __fput+0xa8/0x1e0
> [  133.028901]  ____fput+0x20/0x30
> [  133.032006]  task_work_run+0xa0/0xd0
> [  133.035539]  do_notify_resume+0x118/0x120
> [  133.039503]  work_pending+0x8/0x10
>
> Is a raw_spin_lock_init missing perhaps?

Not that I can tell - I need to investigate.

>
> Thanks,
>
> Kim