[PATCH] add missing mutex lock to amdgpu_get_xgmi_hive() (v2)

[Grodzovsky, Andrey]

On 01/07/2019 11:53 AM, StDenis, Tom wrote:
> On 2019-01-07 11:51 a.m., Grodzovsky, Andrey wrote:
>>
>> On 01/07/2019 11:36 AM, StDenis, Tom wrote:
>>> On 2019-01-07 11:33 a.m., Grodzovsky, Andrey wrote:
>>>> On 01/07/2019 11:16 AM, Liu, Shaoyun wrote:
>>>>> I think it's reasonable to use the hive  specific lock for hive  specific functions.
>>>>> The changes is acked-by  Shaoyun.liu < Shaoyun.liu at amd.com>
>>>>>
>>>>> -----Original Message-----
>>>>> From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org> On Behalf Of StDenis, Tom
>>>>> Sent: Monday, January 7, 2019 10:16 AM
>>>>> To: amd-gfx at lists.freedesktop.org
>>>>> Cc: StDenis, Tom <Tom.StDenis at amd.com>
>>>>> Subject: [PATCH] add missing mutex lock to amdgpu_get_xgmi_hive() (v2)
>>>>>
>>>>> v2: Move locks around in other functions so that this function can stand on its own.  Also only hold the hive specific lock for add/remove device instead of the driver global lock so you can't add/remove devices in parallel from one hive.
>>>>>
>>>>> Signed-off-by: Tom St Denis <tom.stdenis at amd.com>
>>>>> ---
>>>>>       drivers/gpu/drm/amd/amdgpu/amdgpu_device.c |  2 +-
>>>>>       drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.c   | 36 ++++++++++++++--------
>>>>>       drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.h   |  2 +-
>>>>>       3 files changed, 25 insertions(+), 15 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>>> index 39d5d058b2c7..13d8e2ad2f7a 100644
>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>>> @@ -3525,7 +3525,7 @@ int amdgpu_device_gpu_recover(struct amdgpu_device *adev,
>>>>>       	 * by different nodes. No point also since the one node already executing
>>>>>       	 * reset will also reset all the other nodes in the hive.
>>>>>       	 */
>>>>> -	hive = amdgpu_get_xgmi_hive(adev);
>>>>> +	hive = amdgpu_get_xgmi_hive(adev, 0);
>>>>>       	if (hive && adev->gmc.xgmi.num_physical_nodes > 1 &&
>>>>>       	    !mutex_trylock(&hive->hive_lock))
>>>>>       		return 0;
>>>> Let's say i have device 0 in hive A and it just got a gpu reset and at
>>>> the same time device 1 is being added to same have though
>>>> amdgpu_xgmi_add_device, hive->hive_lock is acquired by this new device
>>>> being added and so gpu reset for device 0 bails out on
>>>> '!mutex_trylock(&hive->hive_lock))' without completing the reset.
>>>> Also in general i feel a bit uncomfortable about the confusing
>>>> acquisition scheme in the function and  the fact that you take the
>>>> hive->hive_lock inside amdgpu_get_xgmi_hive but release is still outside
>>>> of the function.
>>> Is adding a device while resetting a device even a valid operation
>>> anyways?
>> In theory it's valid if you have hot pluggable devices
>>> I think this means more so that the reset logic is broken.  Instead
>>> there should be a per-hive reset lock that is taken and that is tested
>>> instead.
>>>
>>> Tom
>> The hive->hive_lock was added exactly for this purpose and used only for
>> that purpose. Maybe the naming i gave it wasn't reflective of it's
>> purpose :)
>
> But the add/remove should use per-hive locks not the global lock... :-)
>
> (I'm honestly not trying to bike shed I just thought the get_hive
> function looked wrong :-)).
>
> Tom

Totally agree with you, if Shayun (who origianlly added the global 
xgmi_mutex) is fine with switching to per hive mutex then me too, I just 
point out the problem with gpu reset and as you said we then need to 
rename the existing hive_lock into reset_lock and then and another per 
hive lock to do what you propose. Also - is there a way to not take the 
hive lock inside amdgpu_get_xgmi_hive but release it outside ? AFAIK 
it's an opening for problems where people use it but forget to call 
release.

Andrey

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