linux-kernel - Re: [PATCH v3 6/9] coresight-funnel: change funnel_drvdata spinlock's type to raw_spinlock

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Message-ID: <CAJ9a7Vju8N=i5s=OUTXdCu8j2d95ZsqYT43jR54v6rui8o3DYw@mail.gmail.com>
Date: Thu, 19 Dec 2024 12:24:30 +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 6/9] coresight-funnel: change funnel_drvdata spinlock's
 type to raw_spinlock_t

On Mon, 16 Dec 2024 at 11:50, Yeoreum Yun <yeoreum.yun@....com> wrote:
>
> In coresight-funnel drivers, cti_drvdata->spinlock can be held
> during __schedule() by perf_event_task_sched_out()/in().
>
> Since funnel_drvdata->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 funnel_drvdata->spinlock in
> coresight-funnel 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/coresight-funnel.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-funnel.c b/drivers/hwtracing/coresight/coresight-funnel.c
> index 33efe1acbef7..a566c8854327 100644
> --- a/drivers/hwtracing/coresight/coresight-funnel.c
> +++ b/drivers/hwtracing/coresight/coresight-funnel.c
> @@ -47,7 +47,7 @@ struct funnel_drvdata {
>         struct clk              *pclk;
>         struct coresight_device *csdev;
>         unsigned long           priority;
> -       spinlock_t              spinlock;
> +       raw_spinlock_t          spinlock;
>  };
>
>  static int dynamic_funnel_enable_hw(struct funnel_drvdata *drvdata, int port)
> @@ -85,7 +85,7 @@ static int funnel_enable(struct coresight_device *csdev,
>         unsigned long flags;
>         bool first_enable = false;
>
> -       spin_lock_irqsave(&drvdata->spinlock, flags);
> +       raw_spin_lock_irqsave(&drvdata->spinlock, flags);
>         if (atomic_read(&in->dest_refcnt) == 0) {
>                 if (drvdata->base)
>                         rc = dynamic_funnel_enable_hw(drvdata, in->dest_port);
> @@ -94,7 +94,7 @@ static int funnel_enable(struct coresight_device *csdev,
>         }
>         if (!rc)
>                 atomic_inc(&in->dest_refcnt);
> -       spin_unlock_irqrestore(&drvdata->spinlock, flags);
> +       raw_spin_unlock_irqrestore(&drvdata->spinlock, flags);
>
>         if (first_enable)
>                 dev_dbg(&csdev->dev, "FUNNEL inport %d enabled\n",
> @@ -129,13 +129,13 @@ static void funnel_disable(struct coresight_device *csdev,
>         unsigned long flags;
>         bool last_disable = false;
>
> -       spin_lock_irqsave(&drvdata->spinlock, flags);
> +       raw_spin_lock_irqsave(&drvdata->spinlock, flags);
>         if (atomic_dec_return(&in->dest_refcnt) == 0) {
>                 if (drvdata->base)
>                         dynamic_funnel_disable_hw(drvdata, in->dest_port);
>                 last_disable = true;
>         }
> -       spin_unlock_irqrestore(&drvdata->spinlock, flags);
> +       raw_spin_unlock_irqrestore(&drvdata->spinlock, flags);
>
>         if (last_disable)
>                 dev_dbg(&csdev->dev, "FUNNEL inport %d disabled\n",
> @@ -266,7 +266,7 @@ static int funnel_probe(struct device *dev, struct resource *res)
>         }
>         dev->platform_data = pdata;
>
> -       spin_lock_init(&drvdata->spinlock);
> +       raw_spin_lock_init(&drvdata->spinlock);
>         desc.type = CORESIGHT_DEV_TYPE_LINK;
>         desc.subtype.link_subtype = CORESIGHT_DEV_SUBTYPE_LINK_MERG;
>         desc.ops = &funnel_cs_ops;
> --
> LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
>

Reviewed-by: Mike Leach <mike.leach@...aro.org>

--
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK