linux-kernel - Re: [PATCH v3 9/9] coresight/ultrasoc: change cti_drvdata spinlock's type to raw_spinlock

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Message-ID: <Z2VB7uGgTpOoRQqj@e129823.arm.com>
Date: Fri, 20 Dec 2024 10:07:42 +0000
From: Yeoreum Yun <yeoreum.yun@....com>
To: Mike Leach <mike.leach@...aro.org>
Cc: suzuki.poulose@....com, james.clark@...aro.org,
	alexander.shishkin@...ux.intel.com, bigeasy@...utronix.de,
	clrkwllms@...nel.org, rostedt@...dmis.org,
	coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev
Subject: Re: [PATCH v3 9/9] coresight/ultrasoc: change cti_drvdata spinlock's
 type to raw_spinlock_t

Hi Mike.

> Title of patch - this patch has nothing to do with cti_drvdata.

Sorry. I'll fix this. Thanks
>
>
> On Mon, 16 Dec 2024 at 11:50, Yeoreum Yun <yeoreum.yun@....com> wrote:
> >
> > In ultrasoc-smb drivers, smb_drv_data->spinlock can be held
> > during __schedule() by perf_event_task_sched_out()/in().
> >
> > Since smb__drv_data->spinlock type is spinlock_t and
> > perf_event_task_sched_out()/in() is called after acquiring rq_lock,
> > which is raw_spinlock_t (an unsleepable lock),
> > this poses an issue in PREEMPT_RT kernel where spinlock_t is sleepable.
> >
> > To address this, change type smb_drv_data->spinlock in ultrasoc-smb drivers,
> > which can be called by perf_event_task_sched_out()/in(),
> > from spinlock_t to raw_spinlock_t.
> >
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
> > ---
> >  drivers/hwtracing/coresight/ultrasoc-smb.c | 12 ++++++------
> >  drivers/hwtracing/coresight/ultrasoc-smb.h |  2 +-
> >  2 files changed, 7 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/ultrasoc-smb.c b/drivers/hwtracing/coresight/ultrasoc-smb.c
> > index dc3c9504dd7c..26cfc939e5bd 100644
> > --- a/drivers/hwtracing/coresight/ultrasoc-smb.c
> > +++ b/drivers/hwtracing/coresight/ultrasoc-smb.c
> > @@ -98,7 +98,7 @@ static int smb_open(struct inode *inode, struct file *file)
> >         struct smb_drv_data *drvdata = container_of(file->private_data,
> >                                         struct smb_drv_data, miscdev);
> >
> > -       guard(spinlock)(&drvdata->spinlock);
> > +       guard(raw_spinlock)(&drvdata->spinlock);
> >
> >         if (drvdata->reading)
> >                 return -EBUSY;
> > @@ -152,7 +152,7 @@ static int smb_release(struct inode *inode, struct file *file)
> >         struct smb_drv_data *drvdata = container_of(file->private_data,
> >                                         struct smb_drv_data, miscdev);
> >
> > -       guard(spinlock)(&drvdata->spinlock);
> > +       guard(raw_spinlock)(&drvdata->spinlock);
> >         drvdata->reading = false;
> >
> >         return 0;
> > @@ -245,7 +245,7 @@ static int smb_enable(struct coresight_device *csdev, enum cs_mode mode,
> >         struct smb_drv_data *drvdata = dev_get_drvdata(csdev->dev.parent);
> >         int ret = 0;
> >
> > -       guard(spinlock)(&drvdata->spinlock);
> > +       guard(raw_spinlock)(&drvdata->spinlock);
> >
> >         /* Do nothing, the trace data is reading by other interface now */
> >         if (drvdata->reading)
> > @@ -280,7 +280,7 @@ static int smb_disable(struct coresight_device *csdev)
> >  {
> >         struct smb_drv_data *drvdata = dev_get_drvdata(csdev->dev.parent);
> >
> > -       guard(spinlock)(&drvdata->spinlock);
> > +       guard(raw_spinlock)(&drvdata->spinlock);
> >
> >         if (drvdata->reading)
> >                 return -EBUSY;
> > @@ -378,7 +378,7 @@ static unsigned long smb_update_buffer(struct coresight_device *csdev,
> >         if (!buf)
> >                 return 0;
> >
> > -       guard(spinlock)(&drvdata->spinlock);
> > +       guard(raw_spinlock)(&drvdata->spinlock);
> >
> >         /* Don't do anything if another tracer is using this sink. */
> >         if (csdev->refcnt != 1)
> > @@ -563,7 +563,7 @@ static int smb_probe(struct platform_device *pdev)
> >
> >         smb_reset_buffer(drvdata);
> >         platform_set_drvdata(pdev, drvdata);
> > -       spin_lock_init(&drvdata->spinlock);
> > +       raw_spin_lock_init(&drvdata->spinlock);
> >         drvdata->pid = -1;
> >
> >         ret = smb_register_sink(pdev, drvdata);
> > diff --git a/drivers/hwtracing/coresight/ultrasoc-smb.h b/drivers/hwtracing/coresight/ultrasoc-smb.h
> > index a91d39cfccb8..c4c111275627 100644
> > --- a/drivers/hwtracing/coresight/ultrasoc-smb.h
> > +++ b/drivers/hwtracing/coresight/ultrasoc-smb.h
> > @@ -115,7 +115,7 @@ struct smb_drv_data {
> >         struct coresight_device *csdev;
> >         struct smb_data_buffer sdb;
> >         struct miscdevice miscdev;
> > -       spinlock_t spinlock;
> > +       raw_spinlock_t spinlock;
> >         bool reading;
> >         pid_t pid;
> >  };
> > --
> > LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
> >
>
>
> --
> Mike Leach
> Principal Engineer, ARM Ltd.
> Manchester Design Centre. UK