lkml.org 
[lkml]   [2018]   [Jun]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v4 05/14] coresight: get/put module in coresight_build/release_path
From
Date
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
>

\
 
 \ /
  Last update: 2018-06-06 11:47    [W:0.053 / U:6.344 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site