linux-kernel - Re: [PATCH v3 7/9] coresight-replicator: change replicator_drvdata spinlock's type to raw_spinlock

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Message-ID: <CAJ9a7Vg_vyyG7A8N=+oUiE2MCPFR4+XGqZBe+Mq8c222Wq6Q8w@mail.gmail.com>
Date: Thu, 19 Dec 2024 12:24:34 +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 7/9] coresight-replicator: change replicator_drvdata
 spinlock's type to raw_spinlock_t

On Mon, 16 Dec 2024 at 11:50, Yeoreum Yun <yeoreum.yun@....com> wrote:
>
> In coresight-replicator drivers, replicator_drvdata->spinlock can be held
> during __schedule() by perf_event_task_sched_out()/in().
>
> Since replicator_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 replicator_drvdata->spinlock in
> coresight-replicator 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-replicator.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-replicator.c b/drivers/hwtracing/coresight/coresight-replicator.c
> index 0fba87de6d1a..7d36fe2176cc 100644
> --- a/drivers/hwtracing/coresight/coresight-replicator.c
> +++ b/drivers/hwtracing/coresight/coresight-replicator.c
> @@ -41,7 +41,7 @@ struct replicator_drvdata {
>         struct clk              *atclk;
>         struct clk              *pclk;
>         struct coresight_device *csdev;
> -       spinlock_t              spinlock;
> +       raw_spinlock_t          spinlock;
>         bool                    check_idfilter_val;
>  };
>
> @@ -125,7 +125,7 @@ static int replicator_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(&out->src_refcnt) == 0) {
>                 if (drvdata->base)
>                         rc = dynamic_replicator_enable(drvdata, in->dest_port,
> @@ -135,7 +135,7 @@ static int replicator_enable(struct coresight_device *csdev,
>         }
>         if (!rc)
>                 atomic_inc(&out->src_refcnt);
> -       spin_unlock_irqrestore(&drvdata->spinlock, flags);
> +       raw_spin_unlock_irqrestore(&drvdata->spinlock, flags);
>
>         if (first_enable)
>                 dev_dbg(&csdev->dev, "REPLICATOR enabled\n");
> @@ -179,14 +179,14 @@ static void replicator_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(&out->src_refcnt) == 0) {
>                 if (drvdata->base)
>                         dynamic_replicator_disable(drvdata, in->dest_port,
>                                                    out->src_port);
>                 last_disable = true;
>         }
> -       spin_unlock_irqrestore(&drvdata->spinlock, flags);
> +       raw_spin_unlock_irqrestore(&drvdata->spinlock, flags);
>
>         if (last_disable)
>                 dev_dbg(&csdev->dev, "REPLICATOR disabled\n");
> @@ -277,7 +277,7 @@ static int replicator_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_SPLIT;
>         desc.ops = &replicator_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