linux-kernel - Re: [PATCH v5 01/13] coresight: Fix loss of connection info when a module is unloaded

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Message-ID: <CAJ9a7VicZH1uqbdtN9ATWh=4tP7P64PEo_DfLDjRC9LJHL6NcQ@mail.gmail.com>
Date:   Wed, 12 Apr 2023 14:12:08 +0100
From:   Mike Leach <mike.leach@...aro.org>
To:     James Clark <james.clark@....com>
Cc:     coresight@...ts.linaro.org, quic_jinlmao@...cinc.com,
        suzuki.poulose@....com,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 01/13] coresight: Fix loss of connection info when a
 module is unloaded

On Tue, 4 Apr 2023 at 16:51, James Clark <james.clark@....com> wrote:
>
> child_fwnode should be a read only property based on the DT or ACPI. If
> it's cleared on the parent device when a child is unloaded, then when
> the child is loaded again the connection won't be remade.
>
> child_dev should be cleared instead which signifies that the connection
> should be remade when the child_fwnode registers a new coresight_device.
>
> Similarly the reference count shouldn't be decremented as long as the
> parent device exists. The correct place to drop the reference is in
> coresight_release_platform_data() which is already done.
>
> Reproducible on Juno with the following steps:
>
>   # load all coresight modules.
>   $ cd /sys/bus/coresight/devices/
>   $ echo 1 > tmc_etr0/enable_sink
>   $ echo 1 > etm0/enable_source
>   # Works fine ^
>
>   $ echo 0 > etm0/enable_source
>   $ rmmod coresight-funnel
>   $ modprobe coresight-funnel
>   $ echo 1 > etm0/enable_source
>   -bash: echo: write error: Invalid argument
>
> Fixes: 37ea1ffddffa ("coresight: Use fwnode handle instead of device names")
> Fixes: 2af89ebacf29 ("coresight: Clear the connection field properly")
> Tested-by: Suzuki K Poulose <suzuki.poulose@....com>
> Signed-off-by: James Clark <james.clark@....com>
> ---
>  drivers/hwtracing/coresight/coresight-core.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index d3bf82c0de1d..5733294ce5cd 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -1419,13 +1419,8 @@ static int coresight_remove_match(struct device *dev, void *data)
>                 if (csdev->dev.fwnode == conn->child_fwnode) {
>                         iterator->orphan = true;
>                         coresight_remove_links(iterator, conn);
> -                       /*
> -                        * Drop the reference to the handle for the remote
> -                        * device acquired in parsing the connections from
> -                        * platform data.
> -                        */
> -                       fwnode_handle_put(conn->child_fwnode);
> -                       conn->child_fwnode = NULL;
> +
> +                       conn->child_dev = NULL;
>                         /* No need to continue */
>                         break;
>                 }
> --
> 2.34.1
>

Reviewed-by: Mike Leach <mike.leach@...aro.org>
-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK