Messages in this thread | | | Subject | Re: [PATCH v4 05/14] coresight: get/put module in coresight_build/release_path | From | Suzuki K Poulose <> | Date | Wed, 6 Jun 2018 10:46:36 +0100 |
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On 06/06/2018 09:24 AM, Greg Kroah-Hartman wrote: > 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.
You're right. We do have coresight_mutex, which is held across the build path and the csdev is removed when a device is unregistered. However, I see that we don't hold the mutex while removing the connections from coresight_unregister(). Holding the mutex should protect us from the csdev being removed, while we build the path.
And while we are at this, I also realised that we hold references to the parent devices for each connection (via bus_find_device() from of_coresight_get_endpoint_device()), while parsing the platform data, which is never released.
Thanks Suzuki
> > thanks, > > greg k-h >
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