Hi Tingwei,
On Sun, 26 Jul 2020 at 02:32, Tingwei Zhang tingweiz@codeaurora.org wrote:
Hi Mike, On Sat, Jul 25, 2020 at 09:51:31PM +0800, Mike Leach wrote:
Hi Tingwei,
On Sat, 25 Jul 2020 at 11:05, Tingwei Zhang tingweiz@codeaurora.org wrote:
Hi Mike,
Thu, Jul 23, 2020 at 06:55:47PM +0800, Mike Leach wrote:
Hi Tingwei,
On Thu, 23 Jul 2020 at 05:28, Tingwei Zhang tingwei@codeaurora.org wrote:
When coresight device is in an active session, driver module of that device should not be removed. Use try_get_module() in coresight_grab_device() to prevent module to be unloaded.
Signed-off-by: Tingwei Zhang tingwei@codeaurora.org
drivers/hwtracing/coresight/coresight.c | 27
+++++++++++++++++++++----
1 file changed, 23 insertions(+), 4 deletions(-)
diff --git a/drivers/hwtracing/coresight/coresight.c
b/drivers/hwtracing/coresight/coresight.c
index b7151c5f81b1..17bc76ea86ae 100644 --- a/drivers/hwtracing/coresight/coresight.c +++ b/drivers/hwtracing/coresight/coresight.c @@ -640,7 +640,7 @@ struct coresight_device
*coresight_get_sink_by_id(u32 id)
- don't appear on the trace path, they should be handled along
with
the
- the master device.
*/ -static void coresight_grab_device(struct coresight_device *csdev) +static int coresight_grab_device(struct coresight_device *csdev) { int i;
@@ -648,10 +648,25 @@ static void coresight_grab_device(struct
coresight_device *csdev)
struct coresight_device *child; child = csdev->pdata->conns[i].child_dev;
if (child && child->type ==CORESIGHT_DEV_TYPE_HELPER)
if (child && child->type ==CORESIGHT_DEV_TYPE_HELPER) {
if(!try_module_get(child->dev.parent->driver->owner))
goto err; pm_runtime_get_sync(child->dev.parent);} }if (!try_module_get(csdev->dev.parent->driver->owner))goto err; pm_runtime_get_sync(csdev->dev.parent);return 0;+err:
for (i--; i >= 0; i--) {struct coresight_device *child;child = csdev->pdata->conns[i].child_dev;if (child && child->type ==CORESIGHT_DEV_TYPE_HELPER)
pm_runtime_put(child->dev.parent);}return -ENODEV;}
/* @@ -663,12 +678,15 @@ static void coresight_drop_device(struct
coresight_device *csdev)
int i; pm_runtime_put(csdev->dev.parent);
module_put(csdev->dev.parent->driver->owner); for (i = 0; i < csdev->pdata->nr_outport; i++) { struct coresight_device *child; child = csdev->pdata->conns[i].child_dev;
if (child && child->type ==CORESIGHT_DEV_TYPE_HELPER)
if (child && child->type ==CORESIGHT_DEV_TYPE_HELPER) {
pm_runtime_put(child->dev.parent);
module_put(child->dev.parent->driver->owner);
} }}
@@ -721,7 +739,8 @@ static int _coresight_build_path(struct
coresight_device *csdev,
if (!node) return -ENOMEM;
coresight_grab_device(csdev);
if (coresight_grab_device(csdev))return -ENODEV; node->csdev = csdev; list_add(&node->link, path);-- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
Forum,
a Linux Foundation Collaborative Project
The CTI devices are associated with other coresight components using csdev->ect_dev; These are not handled in the main linear trace path as these have a star topology interlinking all components. However, when a component has an associated ect_dev then is enabled at the same time as the other component is enabled.
So a module_get/put will be needed for this association to prevent the CTI being removed while a trace session is active. I suggest in coresight.c : coresight_control_assoc_ectdev()
In module unload process, devices of that module will be removed. In this case, cti_remove() is called on all cti device when unloading cti module. All cti connections is cleaned at that time. csdev->ect_dev is set to NULL. coresight_control_assoc_ectdev() will return since since ect_csdev is NULL.
I think we are safe without holding module reference since cti driver has done a pretty good job on clean up.
The issue here is not about clean up. We need to keep all the programmed coresight modules loaded and operational while a coresight trace session is in progress. The CTI can be used to control the generation of trace, trigger trace related events etc. If the module is removed while a session is in progress then this programming is lost and the trace data collected may not be what is expected.
Got your point now. In my opinion, CTI is kinda different to other coresight components since it's optional.
For other components, they have to been there when path is built or the enablement fails. Use can either get a successfully return which means it's good and all devices/modules are there until path is released, or a failed return which means trace session can't be setup.
The module get/put do more than ensure that the system can be enabled. They ensure that no components in the coresight path can be unloaded until all paths in use are released. This ensures that clients do not get the trace system pulled out from underneath - corrupting trace data, and possibly affecting the client program.
In CTI case, there's no garrantee that CTI related to the trace session is there even the enablement is successful.
And there is no guarantee that it is not programmed to perform a key task in controlling the generation of trace.
The entire programmed coresight system must be protected when in use. That includes CTI devices. Otherwise the integrity of the captured trace could be compromised, and indeed there may be no trace captured if this is relying on CTI triggers.
For example, One cti is required for ETM tracing session. If cti module is unloaded before enable that trace session. The enablement will still be successfully done since there's no ect_dev connected at all.
My point is holding cti module reference in enable path won't fix all the problem. Altenatively, user should be aware that unload cti module leads to all cti functioniol failure. With current design, the behavior is consistant on cti. User can unload cti module whenever he wants but it will break the function.
Precisely - and this is what should never be allowed - why can the CTI be used to break the trace system but not other components?
Moving forwards we will see users who simply use pre-programmed settings from client programs such as perf. It may be that some users do not have the credentials to add and remove modules - this could be an admin function where larger systems with multiple sessions are in use.
Regards
Mike
Thanks, Tingwei
Regards
Mike
Let me know if you still think we need hold the module reference.
Thanks, Tingwei
Regards
Mike
-- Mike Leach Principal Engineer, ARM Ltd. Manchester Design Centre. UK
linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
-- Mike Leach Principal Engineer, ARM Ltd. Manchester Design Centre. UK
linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel