Re: [PATCH v2] drm/xe: Remove unwanted mutex locking

[Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>]

On Wed, May 29, 2024 at 04:49:19PM -0400, Rodrigo Vivi wrote:
>On Wed, May 29, 2024 at 11:33:19AM -0700, Niranjana Vishwanathapura wrote:
>> Do not hold xef->exec_queue.lock mutex while parsing the xarray
>> xef->exec_queue.xa in xe_file_close() as it is not needed and
>> will cause an unwanted dependency between this lock and the vm->lock.
>>
>> This lock protects the exec queue lookup and reference taking which
>> doesn't apply to this code path. When FD is closing, IOCTLs presumably
>> can't be modifying the xarray.
>>
>> v2: Update commit text
>>
>> Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
>> Reviewed-by: Matthew Brost <matthew.brost@intel.com>
>> ---
>>  drivers/gpu/drm/xe/xe_device.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
>> index f04b11e45c2d..4cca16f2d4ed 100644
>> --- a/drivers/gpu/drm/xe/xe_device.c
>> +++ b/drivers/gpu/drm/xe/xe_device.c
>> @@ -96,12 +96,11 @@ static void xe_file_close(struct drm_device *dev, struct drm_file *file)
>>  	struct xe_exec_queue *q;
>>  	unsigned long idx;
>>
>> -	mutex_lock(&xef->exec_queue.lock);
>> +	/* No locking needed here */
>
>could you please expand this message here to avoid git-blame+git-show
>when trying to understand 'why not?'!?
>

Ok, posted v3 with added code comments.

Niranjana

>Thanks,
>Rodrigo.
>
>>  	xa_for_each(&xef->exec_queue.xa, idx, q) {
>>  		xe_exec_queue_kill(q);
>>  		xe_exec_queue_put(q);
>>  	}
>> -	mutex_unlock(&xef->exec_queue.lock);
>>  	xa_destroy(&xef->exec_queue.xa);
>>  	mutex_destroy(&xef->exec_queue.lock);
>>  	mutex_lock(&xef->vm.lock);
>> --
>> 2.43.0
>>