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()

Regards

Mike

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.

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

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

Hi Tingwei,

On Tue, 28 Jul 2020 at 02:07, Tingwei Zhang tingweiz@codeaurora.org wrote:

Hi Mike,

On Tue, Jul 28, 2020 at 01:04:21AM +0800, Mike Leach wrote:

...

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.

I agree.

...

...

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.

That's correct. If CTI is not there, the trace may be wrong or no trace as all.

...

...

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?

Sorry - I may not have been clear here - I do not want to make having a CTI mandatory for enabling the trace session - this is an optional component.

We can't prevent user to unload CTI module when there's no active trace session.

Agreed - the same applies to all the other components.

If we don't allow CTI to be not available, we need to check whether CTI is there in build_path routine or coresight enable routine. We need return failure if CTI is not there when user enables the trace session. Currently, coresight framework check associate CTI device, but if CTI deivce is not probed due to probe failure or module unload, coresight framework assume there's no assocaite CTI device and just continue the enablement. It won't return failure.

If we have plan to change CTI check to be mandatory, make the coresight enablement fail if CTI is not there like other trace components. I'm perfect fine to add module_get/module_put for CTI.

If the CTI is present at the time the trace path is created, then it must be enabled, and a failure to enable the CTI fails the entire path enable - this is the operation that is implemented by coresight_control_assoc_ectdev() at this time. If a CTI is not present at the time the trace path is created, then as you have said previously, the ect_dev pointer will be NULL and the check and enable of CTI will be skipped by coresight_control_assoc_ectdev() and have no effect on the trace path.

For the module version, if CTI is present and enabled then the module must be locked so it cannot be removed while the trace is active - this is the only change that is required. So adding get / put module in coresight_control_assoc_ectdev() will lock the module in for the duration that trace is active.

I've tested the code below to ensure that the cti module is correctly locked while trace is active, but can be removed as required when trace is inactive.

Regards

Mike

--------------------------------------------------------------------------------- static int coresight_control_assoc_ectdev(struct coresight_device *csdev, bool enable) { int ect_ret = 0; struct coresight_device *ect_csdev = csdev->ect_dev; struct module *mod;

if (!ect_csdev) return 0;

if ((!ect_ops(ect_csdev)->enable) || (!ect_ops(ect_csdev)->disable)) return 0;

mod = ect_csdev->dev.parent->driver->owner;

if (enable) { if (try_module_get(mod)) { ect_ret = ect_ops(ect_csdev)->enable(ect_csdev); if (ect_ret) module_put(mod); } else ect_ret = -ENODEV; } else { module_put(mod); ect_ret = ect_ops(ect_csdev)->disable(ect_csdev); }

/* output warning if ECT enable is preventing trace operation */ if (ect_ret) dev_info(&csdev->dev, "Associated ECT device (%s) %s failed\n", dev_name(&ect_csdev->dev), enable ? "enable" : "disable"); return ect_ret; } ----------------------------------------------------------------------------------------- Tests:- ----------------------- root@linaro-developer:/home/linaro/scripts# ./trace-sysfs-start.bash Tracing via sysfs enabling etf wait before enable etm enabling etm 0. enabling etm 1. enabling etm 2. enabling etm 3. waiting for trace root@linaro-developer:/home/linaro/scripts# rmmod ../cs-mods/coresight-etm4x.ko rmmod: ERROR: Module coresight_etm4x is in use root@linaro-developer:/home/linaro/scripts# rmmod ../cs-mods/coresight-cti.ko rmmod: ERROR: Module coresight_cti is in use root@linaro-developer:/home/linaro/scripts# ./trace-sysfs-end.bash ending trace disabling etm 0. disabling etm 1. disabling etm 2. disabling etm 3. disabling etf 16+0 records in 16+0 records out 8192 bytes (8.2 kB) copied, 0.000834116 s, 9.8 MB/s root@linaro-developer:/home/linaro/scripts# rmmod ../cs-mods/coresight-cti.ko root@linaro-developer:/home/linaro/scripts# rmmod ../cs-mods/coresight-etm4x.ko root@linaro-developer:/home/linaro/scripts# insmod ../cs-mods/coresight-etm4x.ko root@linaro-developer:/home/linaro/scripts# ./trace-sysfs-start.bash Tracing via sysfs enabling etf wait before enable etm enabling etm 0. enabling etm 1. enabling etm 2. enabling etm 3. waiting for trace root@linaro-developer:/home/linaro/scripts# rmmod ../cs-mods/coresight-etm4x.ko rmmod: ERROR: Module coresight_etm4x is in use root@linaro-developer:/home/linaro/scripts# rmmod ../cs-mods/coresight-cti.ko rmmod: ERROR: Module coresight_cti is not currently loaded root@linaro-developer:/home/linaro/scripts# ./trace-sysfs-end.bash ending trace disabling etm 0. disabling etm 1. disabling etm 2. disabling etm 3. disabling etf 16+0 records in 16+0 records out 8192 bytes (8.2 kB) copied, 0.000819117 s, 10.0 MB/s

}

...

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

-- 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

Hi Tingwei,

On Tue, 28 Jul 2020 at 12:17, Tingwei Zhang tingweiz@codeaurora.org wrote:

Hi Mike, On Tue, Jul 28, 2020 at 06:08:37PM +0800, Mike Leach wrote:

...

Hi Tingwei,

On Tue, 28 Jul 2020 at 02:07, Tingwei Zhang tingweiz@codeaurora.org wrote:

...

Hi Mike,

On Tue, Jul 28, 2020 at 01:04:21AM +0800, Mike Leach wrote:

...

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.

I agree.

...

...

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.

That's correct. If CTI is not there, the trace may be wrong or no trace as all.

...

...

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?

Sorry - I may not have been clear here - I do not want to make having a CTI mandatory for enabling the trace session - this is an optional component.

...

We can't prevent user to unload CTI module when there's no active trace session.

Agreed - the same applies to all the other components.

...

If we don't allow CTI to be not available, we need to check whether CTI is there in build_path routine or coresight enable routine. We need return failure if CTI is not there when user enables the trace session. Currently, coresight framework check associate CTI device, but if CTI deivce is not probed due to probe failure or module unload, coresight framework assume there's no assocaite CTI device and just continue the enablement. It won't return failure.

If we have plan to change CTI check to be mandatory, make the coresight enablement fail if CTI is not there like other trace components. I'm perfect fine to add module_get/module_put for CTI.

If the CTI is present at the time the trace path is created, then it must be enabled, and a failure to enable the CTI fails the entire path enable - this is the operation that is implemented by coresight_control_assoc_ectdev() at this time. If a CTI is not present at the time the trace path is created, then as you have said previously, the ect_dev pointer will be NULL and the check and enable of CTI will be skipped by coresight_control_assoc_ectdev() and have no effect on the trace path.

For the module version, if CTI is present and enabled then the module must be locked so it cannot be removed while the trace is active - this is the only change that is required. So adding get / put module in coresight_control_assoc_ectdev() will lock the module in for the duration that trace is active.

I've tested the code below to ensure that the cti module is correctly locked while trace is active, but can be removed as required when trace is inactive.

Thanks a lot for coming up with the patch and testing it, Mike.

...

Regards

Mike

---

static int coresight_control_assoc_ectdev(struct coresight_device *csdev, bool enable) { int ect_ret = 0; struct coresight_device *ect_csdev = csdev->ect_dev; struct module *mod;

if (!ect_csdev)
    return 0;

if ((!ect_ops(ect_csdev)->enable) || (!ect_ops(ect_csdev)->disable))
    return 0;

mod = ect_csdev->dev.parent->driver->owner;

if (enable) {
    if (try_module_get(mod)) {
        ect_ret = ect_ops(ect_csdev)->enable(ect_csdev);
        if (ect_ret)
            module_put(mod);
    } else
        ect_ret = -ENODEV;
} else {
    module_put(mod);
    ect_ret = ect_ops(ect_csdev)->disable(ect_csdev);
}

If CTI module is removed before enablement of ETM and installed after ETM enablement and before ETM disablement. We have a unbalanced module reference number here. I made one test to prove this with above code.

We may need move module_put() after disable(). Return proper error from disable() to indicate CTI was not enabled before so we can skip module_put().

Tests: db845c:/sys/bus/coresight/devices # echo 1 > tmc_etr0/enable_sink db845c:/sys/bus/coresight/devices # echo 1 > etm1/enable_source db845c:/sys/bus/coresight/devices # rmmod coresight_cti rmmod: failed to unload coresight_cti: Try again 1|db845c:/sys/bus/coresight/devices # echo 0 > etm1/enable_source db845c:/sys/bus/coresight/devices # rmmod coresight_cti db845c:/sys/bus/coresight/devices # echo 1 > etm1/enable_source db845c:/sys/bus/coresight/devices # insmod /data/modules/coresight-cti.ko db845c:/sys/bus/coresight/devices # echo 1 > etm2/enable_source db845c:/sys/bus/coresight/devices # echo 0 > etm1/enable_source db845c:/sys/bus/coresight/devices # rmmod coresight_cti db845c:/sys/bus/coresight/devices #

Above module removal should fail since etm2 is still active now.

Good point. Not sure this is sensible user operation, but it is something that needs to be handled. The issue goes beyond just the module count - the CTI driver has an internal enable/disable refcount that is affected by this too.

I think the best way to handle this late CTI load is to flag which Coresight devices have actually enabled the CTI, and only disable for these. So given a new flag in coresight_device, the following is possible:-

if (enable) { if (try_module_get(mod)) { ect_ret = ect_ops(ect_csdev)->enable(ect_csdev); if (ect_ret) module_put(mod); else csdev->ect_enable = true; } else ect_ret = -ENODEV; } else { if (csdev->ect_enable) { module_put(mod); ect_ret = ect_ops(ect_csdev)->disable(ect_csdev); csdev->ect_enable = false; } }

During testing I have found that removing the etm4x module before the cti module results in a crash. This is due to a bug in the cti driver callback that removes sysfs links - and an issue in the coresight-core where that callback is called. I'll forward detail for all this tomorrow.

Regards

Mike

...

/* output warning if ECT enable is preventing trace operation */
if (ect_ret)
    dev_info(&csdev->dev, "Associated ECT device (%s) %s failed\n",
         dev_name(&ect_csdev->dev),
         enable ? "enable" : "disable");
return ect_ret;

}

Tests:-

root@linaro-developer:/home/linaro/scripts# ./trace-sysfs-start.bash Tracing via sysfs enabling etf wait before enable etm enabling etm 0. enabling etm 1. enabling etm 2. enabling etm 3. waiting for trace root@linaro-developer:/home/linaro/scripts# rmmod ../cs-mods/coresight-etm4x.ko rmmod: ERROR: Module coresight_etm4x is in use root@linaro-developer:/home/linaro/scripts# rmmod ../cs-mods/coresight-cti.ko rmmod: ERROR: Module coresight_cti is in use root@linaro-developer:/home/linaro/scripts# ./trace-sysfs-end.bash ending trace disabling etm 0. disabling etm 1. disabling etm 2. disabling etm 3. disabling etf 16+0 records in 16+0 records out 8192 bytes (8.2 kB) copied, 0.000834116 s, 9.8 MB/s root@linaro-developer:/home/linaro/scripts# rmmod ../cs-mods/coresight-cti.ko root@linaro-developer:/home/linaro/scripts# rmmod ../cs-mods/coresight-etm4x.ko root@linaro-developer:/home/linaro/scripts# insmod ../cs-mods/coresight-etm4x.ko root@linaro-developer:/home/linaro/scripts# ./trace-sysfs-start.bash Tracing via sysfs enabling etf wait before enable etm enabling etm 0. enabling etm 1. enabling etm 2. enabling etm 3. waiting for trace root@linaro-developer:/home/linaro/scripts# rmmod ../cs-mods/coresight-etm4x.ko rmmod: ERROR: Module coresight_etm4x is in use root@linaro-developer:/home/linaro/scripts# rmmod ../cs-mods/coresight-cti.ko rmmod: ERROR: Module coresight_cti is not currently loaded root@linaro-developer:/home/linaro/scripts# ./trace-sysfs-end.bash ending trace disabling etm 0. disabling etm 1. disabling etm 2. disabling etm 3. disabling etf 16+0 records in 16+0 records out 8192 bytes (8.2 kB) copied, 0.000819117 s, 10.0 MB/s

}

...

...

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

-- 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

-- Mike Leach Principal Engineer, ARM Ltd. Manchester Design Centre. UK

Hi Greg,

On Thu, Jul 23, 2020 at 01:07:07PM +0200, Greg Kroah-Hartman wrote:

On Thu, Jul 23, 2020 at 12:27:48PM +0800, Tingwei Zhang 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.

Are you sure this works? Why is it needed at all? Why not just tear down the children properly when a module is removed so that you don't need this at all?

Using the terms parent and child is somewhat ambiguous... This is not a parent-child relationship but simply an association between devices, something like port 1 on device "parent" is connected to port 2 on device "child". The parent-child nomenclature was chosen to reflect that a device appears before another in a coresight path. Otherwise there is no other relation between devices, hence the choice of using try_get_module()/put_module() to prevent drivers from being taken away. I'd be happy to proceed differently but haven't found better options.

Going back to parent/child, we could have chosen left/right, up/down or A/B, all of which are just as confusion.

...

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))
  

Why the child's parent? Why not the child itself?

The device structure of each coresight_device is not associated with a driver. It is there to take advantages of device goodies such as dev.type, dev.group, dev.release and dev.bus. Coresight IP blocks are discovered on the AMBA bus and as such amba_device::dev::driver holds the driver itself. In coresight_register() the association coresigth::dev::parent = amba_device::dev is made.

...

• 		goto err;
  

What about the error given to you here? Why throw that away?

...

	pm_runtime_get_sync(child->dev.parent);

• }
  

  }
• if (!try_module_get(csdev->dev.parent->driver->owner))

• goto err;
  

You don't reduce the child's parent's driver owner module reference here?

Here @parent is referencing the current device. Now that helper devices connected to any of its outgoing ports have been enabled (and a reference count to the helper device driver incremented), a reference count to the current device driver can also be incremented.

I hope this clarify what is going on here. It is a little unorthodox but so is coresight.

Thanks, Mathieu

Ugh, that's a horid sentence :(

...

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;
  

Why not return the error given to you?

thanks,

greg k-h

On Thu, Jul 23, 2020 at 08:18:37PM +0200, Greg Kroah-Hartman wrote:

On Thu, Jul 23, 2020 at 12:04:47PM -0600, Mathieu Poirier wrote:

...

Hi Greg,

On Thu, Jul 23, 2020 at 01:07:07PM +0200, Greg Kroah-Hartman wrote:

...

On Thu, Jul 23, 2020 at 12:27:48PM +0800, Tingwei Zhang 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.

Are you sure this works? Why is it needed at all? Why not just tear down the children properly when a module is removed so that you don't need this at all?

Using the terms parent and child is somewhat ambiguous... This is not a parent-child relationship but simply an association between devices, something like port 1 on device "parent" is connected to port 2 on device "child". The parent-child nomenclature was chosen to reflect that a device appears before another in a coresight path. Otherwise there is no other relation between devices, hence the choice of using try_get_module()/put_module() to prevent drivers from being taken away. I'd be happy to proceed differently but haven't found better options.

Going back to parent/child, we could have chosen left/right, up/down or A/B, all of which are just as confusion.

Ok, thanks.

But this causes confusion for everyone as seen below:

...

...

...

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))
  

Why the child's parent? Why not the child itself?

The device structure of each coresight_device is not associated with a driver. It is there to take advantages of device goodies such as dev.type, dev.group, dev.release and dev.bus. Coresight IP blocks are discovered on the AMBA bus and as such amba_device::dev::driver holds the driver itself. In coresight_register() the association coresigth::dev::parent = amba_device::dev is made.

...

...

• 		goto err;
  

What about the error given to you here? Why throw that away?

...

	pm_runtime_get_sync(child->dev.parent);

• }
  

  }
• if (!try_module_get(csdev->dev.parent->driver->owner))

• goto err;
  

You don't reduce the child's parent's driver owner module reference here?

Here @parent is referencing the current device. Now that helper devices connected to any of its outgoing ports have been enabled (and a reference count to the helper device driver incremented), a reference count to the current device driver can also be incremented.

I mean the fact that your error handling does not seem to roll back the module reference count you got up above in the other loop.

Ah! You were talking about the error condition, while I thought you were referring to the normal execution path. I am in agreement with all your comments on error handling.

Or if it does, it's really really not obvious, and should at the very least, be commented as to how it's all cleaning up properly.

thanks,

greg k-h

On Thu, Jul 23, 2020 at 07:07:07PM +0800, Greg Kroah-Hartman wrote:

On Thu, Jul 23, 2020 at 12:27:48PM +0800, Tingwei Zhang 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.

Are you sure this works? Why is it needed at all? Why not just tear down the children properly when a module is removed so that you don't need this at all?

...

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))

Why the child's parent? Why not the child itself?

...

• 		goto err;
  

What about the error given to you here? Why throw that away?

try_module_get() returns bool which doesn't have error code.

...

	pm_runtime_get_sync(child->dev.parent);

• }
  

  }
• if (!try_module_get(csdev->dev.parent->driver->owner))

• goto err;
  

You don't reduce the child's parent's driver owner module reference here?

I'll fix in next revision.

Ugh, that's a horid sentence :(

...

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;
  

Why not return the error given to you?

Thanks. I will fix it in next revision.

Thanks, Tingwei

thanks,

greg k-h