[PATCH] drm/amdkfd: add schedule to remove RCU stall on CPU

[James Zhu]

-Remove others, continue discussing internally

On 2023-08-11 17:12, Chen, Xiaogang wrote:
>
> I know the original jira ticket. The system got RCU cpu stall, then 
> kernel enter panic, then no response or ssh. This patch let prange 
> list update task yield cpu after each range update. It can prevent 
> task holding mm lock too long. mm lock is rw_semophore, not RCU 
> mechanism. Can you explain how that can prevent RCU cpu stall in this 
> case?
[JZ] I can't find exactly rcu_read_lock either, there are many different 
lockers protecting this period.  mm lock is rw_semaphore , i suspected 
it is implemented with RCU mechanism somewhere,
>
> Regards
>
> Xiaogang
>
> On 8/11/2023 2:11 PM, James Zhu wrote:
>> Caution: This message originated from an External Source. Use proper 
>> caution when opening attachments, clicking links, or responding.
>>
>>
>> update_list could be big in list_for_each_entry(prange, &update_list, 
>> update_list),
>> mmap_read_lock(mm) is kept hold all the time, adding schedule() can 
>> remove
>> RCU stall on CPU for this case.
>>
>> RIP: 0010:svm_range_cpu_invalidate_pagetables+0x317/0x610 [amdgpu]
>> Code: 00 00 00 bf 00 02 00 00 48 81 c2 90 00 00 00 e8 1f 6a b9 e0 65 
>> 48 8b 14 25 00 bd 01 00 8b 42 2c 48 8b 3c 24 80 e4 f7 0b 43 d8 <89> 
>> 42 2c e8 51 dd 2d e1 48 8b 7b 38 e8 98 29 b7 e0 48 83 c4 30 b8
>> RSP: 0018:ffffc9000ffd7b10 EFLAGS: 00000206
>> RAX: 0000000000000100 RBX: ffff88c493968d80 RCX: ffff88d1a6469b18
>> RDX: ffff88e18ef1ec80 RSI: ffffc9000ffd7be0 RDI: ffff88c493968d38
>> RBP: 000000000003062e R08: 000000003042f000 R09: 000000003062efff
>> R10: 0000000000001000 R11: ffff88c1ad255000 R12: 000000000003042f
>> R13: ffff88c493968c00 R14: ffffc9000ffd7be0 R15: ffff88c493968c00
>> __mmu_notifier_invalidate_range_start+0x132/0x1d0
>> ? amdgpu_vm_bo_update+0x3fd/0x520 [amdgpu]
>> migrate_vma_setup+0x6c7/0x8f0
>> ? kfd_smi_event_migration_start+0x5f/0x80 [amdgpu]
>> svm_migrate_ram_to_vram+0x14e/0x580 [amdgpu]
>> svm_range_set_attr+0xe34/0x11a0 [amdgpu]
>> kfd_ioctl+0x271/0x4e0 [amdgpu]
>> ? kfd_ioctl_set_xnack_mode+0xd0/0xd0 [amdgpu]
>> __x64_sys_ioctl+0x92/0xd0
>>
>> Signed-off-by: James Zhu <James.Zhu at amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c 
>> b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>> index 113fd11aa96e..9f2d48ade7fa 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>> @@ -3573,6 +3573,7 @@ svm_range_set_attr(struct kfd_process *p, 
>> struct mm_struct *mm,
>>                  r = svm_range_trigger_migration(mm, prange, &migrated);
>>                  if (r)
>>                          goto out_unlock_range;
>> +               schedule();
>>
>>                  if (migrated && (!p->xnack_enabled ||
>>                      (prange->flags & 
>> KFD_IOCTL_SVM_FLAG_GPU_ALWAYS_MAPPED)) &&
>> -- 
>> 2.34.1
>>