| Message ID | 20180605210710.22227-6-kim.phillips@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 06/05/2018 10:07 PM, 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. > > 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)) { > + dev_err(&csdev->dev, "could not get coresight driver module\n"); > + return -ENODEV; > + } > + Kim, It would be safer to do the check before we actually add the device to the path above. That way, we don't add an unavailable device to the path, which will be "released" in the release_path below. Otherwise looks good to me. > pm_runtime_get_sync(csdev->dev.parent); > > return 0; > @@ -510,6 +516,9 @@ void coresight_release_path(struct list_head *path) > csdev = nd->csdev; > > pm_runtime_put_sync(csdev->dev.parent); > + > + module_put(csdev->dev.parent->driver->owner); > + > list_del(&nd->link); > kfree(nd); > } > Suzuki
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
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 >
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)) { + dev_err(&csdev->dev, "could not get coresight driver module\n"); + return -ENODEV; + } + pm_runtime_get_sync(csdev->dev.parent); return 0; @@ -510,6 +516,9 @@ void coresight_release_path(struct list_head *path) csdev = nd->csdev; pm_runtime_put_sync(csdev->dev.parent); + + module_put(csdev->dev.parent->driver->owner); + list_del(&nd->link); kfree(nd); }
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. 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(+)