linux-kernel - Re: [2/2] coresight: Fix reference count for software sources

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Message-ID: <CANLsYkwg_PRcL5Sqd15phOFS-L8-v3SdvF1kBFa9De-==tx9gw@mail.gmail.com>
Date:   Tue, 14 Mar 2017 11:40:44 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     "Suzuki K. Poulose" <Suzuki.Poulose@....com>
Cc:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Chunyan Zhang <zhang.chunyan@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [2/2] coresight: Fix reference count for software sources

On 14 March 2017 at 11:32, Mathieu Poirier <mathieu.poirier@...aro.org> wrote:
> From: "Suzuki K. Poulose" <Suzuki.Poulose@....com>
>
> For software sources (i.e STM), there could be multiple agents
> generating the trace data, unlike the ETMs. So we need to
> properly do the accounting for the active number of users
> to disable the device when the last user goes away. Right
> now, the reference counting is broken for sources as we skip
> the actions when we detect that the source is enabled.
>
> This patch fixes the problem by adding the refcounting for
> software sources, even when they are enabled.
>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Reported-by: Robert Walker <robert.walker@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>  drivers/hwtracing/coresight/coresight.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c
> index 34cd1ed..2da9e39 100644
> --- a/drivers/hwtracing/coresight/coresight.c
> +++ b/drivers/hwtracing/coresight/coresight.c
> @@ -552,6 +552,7 @@ int coresight_enable(struct coresight_device *csdev)
>         int cpu, ret = 0;
>         struct coresight_device *sink;
>         struct list_head *path;
> +       enum coresight_dev_subtype_source subtype = csdev->subtype.source_subtype;

Checkpatch.pl complains about a line over 80 characters.

>
>         mutex_lock(&coresight_mutex);
>
> @@ -559,8 +560,16 @@ int coresight_enable(struct coresight_device *csdev)
>         if (ret)
>                 goto out;
>
> -       if (csdev->enable)
> +       if (csdev->enable) {
> +               /*
> +                * There could be multiple applications driving the software
> +                * source. So keep the refcount for each such user when the
> +                * source is already enabled.
> +                */
> +               if (subtype == CORESIGHT_DEV_SUBTYPE_SOURCE_SOFTWARE)
> +                       atomic_inc(csdev->refcnt);
>                 goto out;
> +       }
>
>         /*
>          * Search for a valid sink for this session but don't reset the
> @@ -587,7 +596,7 @@ int coresight_enable(struct coresight_device *csdev)
>         if (ret)
>                 goto err_source;
>
> -       switch (csdev->subtype.source_subtype) {
> +       switch (subtype) {
>         case CORESIGHT_DEV_SUBTYPE_SOURCE_PROC:
>                 /*
>                  * When working from sysFS it is important to keep track