On Wed, 6 Jun 2018 10:46:36 +0100 Suzuki K Poulose <[email protected]> wrote:
> 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 <[email protected]> > >> Cc: Leo Yan <[email protected]> > >> Cc: Alexander Shishkin <[email protected]> > >> Cc: Randy Dunlap <[email protected]> > >> Cc: Suzuki K Poulose <[email protected]> > >> Cc: Greg Kroah-Hartman <[email protected]> > >> Cc: Russell King <[email protected]> > >> Signed-off-by: Kim Phillips <[email protected]> > >> --- > >> 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. OK, I'll add this for the next version: diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c index f96258de1e9b..da702507a55c 100644 --- a/drivers/hwtracing/coresight/coresight-core.c +++ b/drivers/hwtracing/coresight/coresight-core.c @@ -1040,8 +1040,12 @@ EXPORT_SYMBOL_GPL(coresight_register); void coresight_unregister(struct coresight_device *csdev) { + mutex_lock(&coresight_mutex); + /* Remove references of that device in the topology */ coresight_remove_conns(csdev); device_unregister(&csdev->dev); + + mutex_unlock(&coresight_mutex); } EXPORT_SYMBOL_GPL(coresight_unregister); > 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. Would this fix that?: diff --git a/drivers/hwtracing/coresight/of_coresight.c b/drivers/hwtracing/coresight/of_coresight.c index a33a92ebe74b..a43ab078c85e 100644 --- a/drivers/hwtracing/coresight/of_coresight.c +++ b/drivers/hwtracing/coresight/of_coresight.c @@ -181,6 +181,8 @@ of_get_coresight_platform_data(struct device *dev, pdata->child_names[i] = dev_name(rdev); pdata->child_ports[i] = rendpoint.id; + put_device(rdev); + i++; } while (ep); } Thanks, Kim
