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

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Message-ID: <CAJ9a7ViC+ZSzNYTo+mKK4UYw=GBO9TCyJ2WHN879=hO-tq8JvQ@mail.gmail.com>
Date: Thu, 19 Dec 2024 12:24:26 +0000
From: Mike Leach <mike.leach@...aro.org>
To: Yeoreum Yun <yeoreum.yun@....com>
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

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

Mike


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