[PATCH 4/6] drm/amdkfd: GFP_NOIO while holding locks taken in MMU notifier

[Felix Kuehling]

On 2018-05-11 03:59 AM, Oded Gabbay wrote:
> On Fri, Mar 23, 2018 at 10:32 PM, Felix Kuehling <Felix.Kuehling at amd.com> wrote:
>> When an MMU notifier runs in memory reclaim context, it can deadlock
>> trying to take locks that are already held in the thread causing the
>> memory reclaim. The solution is to avoid memory reclaim while holding
>> locks that are taken in MMU notifiers by using GFP_NOIO.
> Which locks are problematic ?

The only lock I need to take in our MMU notifier is the DQM lock.

>
> The kernel recommendation is to use "memalloc_noio_{save,restore} to
> mark the whole scope which cannot perform any IO with a short
> explanation why"

Yeah. Looking at it more, I think the correct one to use is actually
memalloc_nofs_{save,restore}.

>
> By using the scope functions, you protect against future allocation
> code that will be written in the critical path, without worrying about
> the developer using the correct GFP_NOIO flag.

Yes. Last time I looked into this it was broken and didn't properly
handle kmalloc allocations. It looks like this was fixed by this commit:

    commit 6d7225f0cc1a1fc32cf5dd01b4ab4b8a34c7cdb4
    Author: Nikolay Borisov <nborisov at suse.com>
    Date:   Wed May 3 14:53:05 2017 -0700

        lockdep: teach lockdep about memalloc_noio_save


Later NOFS was introduced, which is now used by the lockdep checker to
detect reclaim deadlocks.

Regards,
  Felix

>
> Oded
>
>> This commit fixes memory allocations done while holding the dqm->lock
>> which is needed in the MMU notifier (dqm->ops.evict_process_queues).
>>
>> Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
>> ---
>>  drivers/gpu/drm/amd/amdkfd/kfd_device.c          | 2 +-
>>  drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_cik.c | 2 +-
>>  drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_vi.c  | 2 +-
>>  3 files changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_device.c b/drivers/gpu/drm/amd/amdkfd/kfd_device.c
>> index 334669996..0434f65 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_device.c
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_device.c
>> @@ -652,7 +652,7 @@ int kfd_gtt_sa_allocate(struct kfd_dev *kfd, unsigned int size,
>>         if (size > kfd->gtt_sa_num_of_chunks * kfd->gtt_sa_chunk_size)
>>                 return -ENOMEM;
>>
>> -       *mem_obj = kmalloc(sizeof(struct kfd_mem_obj), GFP_KERNEL);
>> +       *mem_obj = kmalloc(sizeof(struct kfd_mem_obj), GFP_NOIO);
>>         if ((*mem_obj) == NULL)
>>                 return -ENOMEM;
>>
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_cik.c b/drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_cik.c
>> index c00c325..2bc49c6 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_cik.c
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_cik.c
>> @@ -412,7 +412,7 @@ struct mqd_manager *mqd_manager_init_cik(enum KFD_MQD_TYPE type,
>>         if (WARN_ON(type >= KFD_MQD_TYPE_MAX))
>>                 return NULL;
>>
>> -       mqd = kzalloc(sizeof(*mqd), GFP_KERNEL);
>> +       mqd = kzalloc(sizeof(*mqd), GFP_NOIO);
>>         if (!mqd)
>>                 return NULL;
>>
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_vi.c b/drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_vi.c
>> index 89e4242..481307b 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_vi.c
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_vi.c
>> @@ -394,7 +394,7 @@ struct mqd_manager *mqd_manager_init_vi(enum KFD_MQD_TYPE type,
>>         if (WARN_ON(type >= KFD_MQD_TYPE_MAX))
>>                 return NULL;
>>
>> -       mqd = kzalloc(sizeof(*mqd), GFP_KERNEL);
>> +       mqd = kzalloc(sizeof(*mqd), GFP_NOIO);
>>         if (!mqd)
>>                 return NULL;
>>
>> --
>> 2.7.4
>>