linux-kernel - Re: [PATCH v3] coresight: tmc-etr: Fix perf

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Date:   Mon, 19 Aug 2019 16:55:26 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Yabin Cui <yabinc@...gle.com>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] coresight: tmc-etr: Fix perf_data check.

On Thu, 15 Aug 2019 at 12:46, Yabin Cui <yabinc@...gle.com> wrote:
>
> When tracing etm data of multiple threads on multiple cpus through
> perf interface, each cpu has a unique etr_perf_buffer while sharing
> the same etr device. There is no guarantee that the last cpu starts
> etm tracing also stops last. This makes perf_data check fail.
>
> Fix it by checking etr_buf instead of etr_perf_buffer.
> Also move the code setting and clearing perf_buf to more suitable
> places.
>
> Fixes: 3147da92a8a8 ("coresight: tmc-etr: Allocate and free ETR memory buffers for CPU-wide scenarios")
> Signed-off-by: Yabin Cui <yabinc@...gle.com>
> ---
>
> v2 -> v3:
>   moved place of setting drvdata->perf_buf based on review comment.
>   Also moved place of clearing drvdata->perf_buf from
>   tmc_update_etr_buffer() to tmc_disable_etr_sink() for below
>   situation:
>
>   cpu 0 enable etr device (set perf_buf)
>   cpu 0 update etr buffer (clear perf_buf)
>   cpu 1 enable etr device (perf_buf isn't set because pid set by cpu 0)
>   cpu 0 disable etr device
>   cpu 1 update etr buffer (perf_buf == NULL, check fails)
>
>   To fix it, we need to move clearing perf_buf to the disable function.
>
> ---
>  drivers/hwtracing/coresight/coresight-tmc-etr.c | 8 ++++----
>  drivers/hwtracing/coresight/coresight-tmc.h     | 6 +++---
>  2 files changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> index 17006705287a..80af313f55d7 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> @@ -1484,7 +1484,7 @@ tmc_update_etr_buffer(struct coresight_device *csdev,
>                 goto out;
>         }
>
> -       if (WARN_ON(drvdata->perf_data != etr_perf)) {
> +       if (WARN_ON(drvdata->perf_buf != etr_buf)) {
>                 lost = true;
>                 spin_unlock_irqrestore(&drvdata->spinlock, flags);
>                 goto out;
> @@ -1496,8 +1496,6 @@ tmc_update_etr_buffer(struct coresight_device *csdev,
>         tmc_sync_etr_buf(drvdata);
>
>         CS_LOCK(drvdata->base);
> -       /* Reset perf specific data */
> -       drvdata->perf_data = NULL;
>         spin_unlock_irqrestore(&drvdata->spinlock, flags);
>
>         size = etr_buf->len;
> @@ -1556,7 +1554,6 @@ static int tmc_enable_etr_sink_perf(struct coresight_device *csdev, void *data)
>         }
>
>         etr_perf->head = PERF_IDX2OFF(handle->head, etr_perf);
> -       drvdata->perf_data = etr_perf;
>
>         /*
>          * No HW configuration is needed if the sink is already in
> @@ -1572,6 +1569,7 @@ static int tmc_enable_etr_sink_perf(struct coresight_device *csdev, void *data)
>                 /* Associate with monitored process. */
>                 drvdata->pid = pid;
>                 drvdata->mode = CS_MODE_PERF;
> +               drvdata->perf_buf = etr_perf->etr_buf;
>                 atomic_inc(csdev->refcnt);
>         }
>
> @@ -1617,6 +1615,8 @@ static int tmc_disable_etr_sink(struct coresight_device *csdev)
>         /* Dissociate from monitored process. */
>         drvdata->pid = -1;
>         drvdata->mode = CS_MODE_DISABLED;
> +       /* Reset perf specific data */
> +       drvdata->perf_buf = NULL;
>
>         spin_unlock_irqrestore(&drvdata->spinlock, flags);
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc.h b/drivers/hwtracing/coresight/coresight-tmc.h
> index 1ed50411cc3c..f9a0c95e9ba2 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc.h
> +++ b/drivers/hwtracing/coresight/coresight-tmc.h
> @@ -178,8 +178,8 @@ struct etr_buf {
>   *             device configuration register (DEVID)
>   * @idr:       Holds etr_bufs allocated for this ETR.
>   * @idr_mutex: Access serialisation for idr.
> - * @perf_data: PERF buffer for ETR.
> - * @sysfs_data:        SYSFS buffer for ETR.
> + * @sysfs_buf: SYSFS buffer for ETR.
> + * @perf_buf:  PERF buffer for ETR.
>   */
>  struct tmc_drvdata {
>         void __iomem            *base;
> @@ -202,7 +202,7 @@ struct tmc_drvdata {
>         struct idr              idr;
>         struct mutex            idr_mutex;
>         struct etr_buf          *sysfs_buf;
> -       void                    *perf_data;
> +       struct etr_buf          *perf_buf;
>  };

I have applied your patch.

Thanks,
Mathieu

>
>  struct etr_buf_operations {
> --
> 2.23.0.rc1.153.gdeed80330f-goog
>