linux-kernel - Re: [PATCH v4 1/2] coresight: catu: Introduce refcount and spinlock for enabling/disabling

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Message-ID: <CALJ9ZPN+JoL1SCoWhgRvCkTa6YPv-psGgOoxL9aotNmbdS+cHA@mail.gmail.com>
Date: Wed, 23 Apr 2025 10:06:50 -0700
From: Yabin Cui <yabinc@...gle.com>
To: Leo Yan <leo.yan@....com>
Cc: Suzuki K Poulose <suzuki.poulose@....com>, Mike Leach <mike.leach@...aro.org>, 
	James Clark <james.clark@...aro.org>, Jie Gan <quic_jiegan@...cinc.com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, coresight@...ts.linaro.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] coresight: catu: Introduce refcount and spinlock
 for enabling/disabling

On Wed, Apr 23, 2025 at 1:16 AM Leo Yan <leo.yan@....com> wrote:
>
> Hi Yabin,
>
> Sorry for late reply as I was on vacation for the past two weeks.
>
> On Tue, Apr 15, 2025 at 11:46:48AM -0700, Yabin Cui wrote:
> > When tracing ETM data on multiple CPUs concurrently via the
> > perf interface, the CATU device is shared across different CPU
> > paths. This can lead to race conditions when multiple CPUs attempt
> > to enable or disable the CATU device simultaneously.
> >
> > To address these race conditions, this patch introduces the
> > following changes:
> >
> > 1. The enable and disable operations for the CATU device are not
> >    reentrant. Therefore, a spinlock is added to ensure that only
> >    one CPU can enable or disable a given CATU device at any point
> >    in time.
> >
> > 2. A reference counter is used to manage the enable/disable state
> >    of the CATU device. The device is enabled when the first CPU
> >    requires it and is only disabled when the last CPU finishes
> >    using it. This ensures the device remains active as long as at
> >    least one CPU needs it.
> >
> > Signed-off-by: Yabin Cui <yabinc@...gle.com>
>
> LGTM:
>
> Reviewed-by: Leo Yan <leo.yan@....com>
>
> As Jie reminded, please add James' review tag in next spin.

Sorry for forgetting to add Reviewed-by. Will add it in next spin.

>
> Thanks,
> Leo
>
> > ---
> >  drivers/hwtracing/coresight/coresight-catu.c | 25 +++++++++++++-------
> >  drivers/hwtracing/coresight/coresight-catu.h |  1 +
> >  2 files changed, 18 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-catu.c b/drivers/hwtracing/coresight/coresight-catu.c
> > index fa170c966bc3..3909b562b077 100644
> > --- a/drivers/hwtracing/coresight/coresight-catu.c
> > +++ b/drivers/hwtracing/coresight/coresight-catu.c
> > @@ -458,12 +458,17 @@ static int catu_enable_hw(struct catu_drvdata *drvdata, enum cs_mode cs_mode,
> >  static int catu_enable(struct coresight_device *csdev, enum cs_mode mode,
> >                      void *data)
> >  {
> > -     int rc;
> > +     int rc = 0;
> >       struct catu_drvdata *catu_drvdata = csdev_to_catu_drvdata(csdev);
> >
> > -     CS_UNLOCK(catu_drvdata->base);
> > -     rc = catu_enable_hw(catu_drvdata, mode, data);
> > -     CS_LOCK(catu_drvdata->base);
> > +     guard(raw_spinlock_irqsave)(&catu_drvdata->spinlock);
> > +     if (csdev->refcnt == 0) {
> > +             CS_UNLOCK(catu_drvdata->base);
> > +             rc = catu_enable_hw(catu_drvdata, mode, data);
> > +             CS_LOCK(catu_drvdata->base);
> > +     }
> > +     if (!rc)
> > +             csdev->refcnt++;
> >       return rc;
> >  }
> >
> > @@ -486,12 +491,15 @@ static int catu_disable_hw(struct catu_drvdata *drvdata)
> >
> >  static int catu_disable(struct coresight_device *csdev, void *__unused)
> >  {
> > -     int rc;
> > +     int rc = 0;
> >       struct catu_drvdata *catu_drvdata = csdev_to_catu_drvdata(csdev);
> >
> > -     CS_UNLOCK(catu_drvdata->base);
> > -     rc = catu_disable_hw(catu_drvdata);
> > -     CS_LOCK(catu_drvdata->base);
> > +     guard(raw_spinlock_irqsave)(&catu_drvdata->spinlock);
> > +     if (--csdev->refcnt == 0) {
> > +             CS_UNLOCK(catu_drvdata->base);
> > +             rc = catu_disable_hw(catu_drvdata);
> > +             CS_LOCK(catu_drvdata->base);
> > +     }
> >       return rc;
> >  }
> >
> > @@ -550,6 +558,7 @@ static int __catu_probe(struct device *dev, struct resource *res)
> >       dev->platform_data = pdata;
> >
> >       drvdata->base = base;
> > +     raw_spin_lock_init(&drvdata->spinlock);
> >       catu_desc.access = CSDEV_ACCESS_IOMEM(base);
> >       catu_desc.pdata = pdata;
> >       catu_desc.dev = dev;
> > diff --git a/drivers/hwtracing/coresight/coresight-catu.h b/drivers/hwtracing/coresight/coresight-catu.h
> > index 141feac1c14b..755776cd19c5 100644
> > --- a/drivers/hwtracing/coresight/coresight-catu.h
> > +++ b/drivers/hwtracing/coresight/coresight-catu.h
> > @@ -65,6 +65,7 @@ struct catu_drvdata {
> >       void __iomem *base;
> >       struct coresight_device *csdev;
> >       int irq;
> > +     raw_spinlock_t spinlock;
> >  };
> >
> >  #define CATU_REG32(name, offset)                                     \
> > --
> > 2.49.0.604.gff1f9ca942-goog
> >