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SubjectRe: [PATCH v4 05/14] coresight: get/put module in coresight_build/release_path
On Tue, Jun 05, 2018 at 04:07:01PM -0500, Kim Phillips wrote:
> Increment the refcnt for driver modules in current use by calling
> module_get in coresight_build_path and module_put in release_path.
>
> This prevents driver modules from being unloaded when they are in use,
> either in sysfs or perf mode.

Why does it matter? Shouldn't you be allowed to remove any module at
any point in time, much like a networking driver?


>
> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> Cc: Leo Yan <leo.yan@linaro.org>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: Randy Dunlap <rdunlap@infradead.org>
> Cc: Suzuki K Poulose <Suzuki.Poulose@arm.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Russell King <linux@armlinux.org.uk>
> Signed-off-by: Kim Phillips <kim.phillips@arm.com>
> ---
> drivers/hwtracing/coresight/coresight.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c
> index 338f1719641c..1c941351f1d1 100644
> --- a/drivers/hwtracing/coresight/coresight.c
> +++ b/drivers/hwtracing/coresight/coresight.c
> @@ -465,6 +465,12 @@ static int _coresight_build_path(struct coresight_device *csdev,
>
> node->csdev = csdev;
> list_add(&node->link, path);
> +
> + if (!try_module_get(csdev->dev.parent->driver->owner)) {

What is to keep parent->driver from going away right here? What keeps
parent around? This feels very fragile to me, I don't see any locking
anywhere around this code path to try to keep things in place.

thanks,

greg k-h

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