Re: [PATCH] drm/amdkfd: Fix false positive queue buffer free warning

[Philip Yang <yangp@amd.com>]

On 2025-10-14 15:46, Felix Kuehling wrote:
>
> On 2025-10-10 15:33, Philip Yang wrote:
>> If active queue buffer is freed, kfd_lookup_process_by_mm return NULL,
>> means process exited and mm is gone, it is fine to evict queue then
>> free queue buffer CPU mapping and memory from do_exit.
>
> In that case, kfd2kgd_quiesce_mm will also fail with -ESRCH. I'm 
> surprised you're getting here at all. I would have expected the queues 
> to be already stopped when the process is gone. But it seems that's 
> only done in the kfd_process_wq_release worker. So is there a time 
> window where the queues are still running, but the queue mappings are 
> destroyed and the queues can't be stopped because we can't look up the 
> process from mm any more?
yes, we should only show warning message if process mm is still alive 
when queue buffer is freed and evict the queues.
>
> Maybe we need to stop the queues in kfd_process_notifier_release to be 
> safe. It should only need the DQM lock, which should be safe to take 
> in an MMU notifiers context.

There is race that queue is running when svm is unmapped on CPU,will add 
another patch in v2 to stop user queues when mm release notifier.

Thanks.

Philip

>
> Regards,
>   Felix
>
>
>>
>> Only show warning message if process mm is still alive when queue
>> buffer is freed.
>>
>> Fixes: b049504e211e ("drm/amdkfd: Validate user queue svm memory 
>> residency")
>> Signed-off-by: Philip Yang <Philip.Yang@amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 15 ++++++++++++---
>>   1 file changed, 12 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c 
>> b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>> index 48c9a211e415..9174f718482a 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>> @@ -2487,17 +2487,26 @@ svm_range_unmap_from_cpu(struct mm_struct 
>> *mm, struct svm_range *prange,
>>       bool unmap_parent;
>>       uint32_t i;
>>   +    p = kfd_lookup_process_by_mm(mm);
>> +
>>       if (atomic_read(&prange->queue_refcount)) {
>>           int r;
>>   -        pr_warn("Freeing queue vital buffer 0x%lx, queue evicted\n",
>> -            prange->start << PAGE_SHIFT);
>> +        /*
>> +         * Evict queue if queue buffer freed with warning message.
>> +         * If process is not found, this is free CPU mapping from
>> +         * do_exit, then it is fine to free queue buffer.
>> +         */
>> +        if (p) {
>> +            pr_warn("Freeing queue vital buffer 0x%lx, queue 
>> evicted\n",
>> +                prange->start << PAGE_SHIFT);
>> +        }
>> +
>>           r = kgd2kfd_quiesce_mm(mm, KFD_QUEUE_EVICTION_TRIGGER_SVM);
>>           if (r)
>>               pr_debug("failed %d to quiesce KFD queues\n", r);
>>       }
>>   -    p = kfd_lookup_process_by_mm(mm);
>>       if (!p)
>>           return;
>>       svms = &p->svms;