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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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