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.
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
