Re: [PATCH v2 0/2] Fix a hung during memory pressure test

Christian König Mon, 06 Sep 2021 02:04:27 -0700



Am 06.09.21 um 03:12 schrieb xinhui pan:

A long time ago, someone reports system got hung during memory test.
In recent days, I am trying to look for or understand the potential
deadlock in ttm/amdgpu code.

This patchset aims to fix the deadlock during ttm populate.

TTM has a parameter called pages_limit, when allocated GTT memory
reaches this limit, swapout would be triggered. As ttm_bo_swapout does
not return the correct retval, populate might get hung.

UVD ib test uses GTT which might be insufficient. So a gpu recovery
would hung if populate hung.


Ah, now I understand what you are trying to do.

Problem is that won't work either. Allocating VRAM can easily land youinside the same deadlock.


We need to avoid the allocation altogether for this for work correctly.


I have made one drm test which alloc two GTT BOs, submit gfx copy
commands and free these BOs without waiting fence. What's more, these
gfx copy commands will cause gfx ring hang. So gpu recovery would be
triggered.

Mhm, that should never be possible. It is perfectly valid for anapplication to terminate without waitting for the GFX submission to becompleted.


Going to push patch #1 to drm-misc-fixes or drm-misc-next-fixes in a moment.

Thanks,
Christian.


Now here is one possible deadlock case.
gpu_recovery
  -> stop drm scheduler
  -> asic reset
    -> ib test
       -> tt populate (uvd ib test)
        ->  ttm_bo_swapout (BO A) // this always fails as the fence of
        BO A would not be signaled by schedluer or HW. Hit deadlock.

I paste the drm test patch below.
#modprobe ttm pages_limit=65536
#amdgpu_test -s 1 -t 4
---
  tests/amdgpu/basic_tests.c | 32 ++++++++++++++------------------
  1 file changed, 14 insertions(+), 18 deletions(-)

diff --git a/tests/amdgpu/basic_tests.c b/tests/amdgpu/basic_tests.c
index dbf02fee..f85ed340 100644
--- a/tests/amdgpu/basic_tests.c
+++ b/tests/amdgpu/basic_tests.c
@@ -65,13 +65,16 @@ static void amdgpu_direct_gma_test(void);
  static void amdgpu_command_submission_write_linear_helper(unsigned ip_type);
  static void amdgpu_command_submission_const_fill_helper(unsigned ip_type);
  static void amdgpu_command_submission_copy_linear_helper(unsigned ip_type);
-static void amdgpu_test_exec_cs_helper(amdgpu_context_handle context_handle,
+static void _amdgpu_test_exec_cs_helper(amdgpu_context_handle context_handle,
                                       unsigned ip_type,
                                       int instance, int pm4_dw, uint32_t 
*pm4_src,
                                       int res_cnt, amdgpu_bo_handle *resources,
                                       struct amdgpu_cs_ib_info *ib_info,
-                                      struct amdgpu_cs_request *ibs_request);
+                                      struct amdgpu_cs_request *ibs_request, 
int sync, int repeat);

+#define amdgpu_test_exec_cs_helper(...) \

+       _amdgpu_test_exec_cs_helper(__VA_ARGS__, 1, 1)
+
  CU_TestInfo basic_tests[] = {
        { "Query Info Test",  amdgpu_query_info_test },
        { "Userptr Test",  amdgpu_userptr_test },
@@ -1341,12 +1344,12 @@ static void amdgpu_command_submission_compute(void)
   * pm4_src, resources, ib_info, and ibs_request
   * submit command stream described in ibs_request and wait for this IB 
accomplished
   */
-static void amdgpu_test_exec_cs_helper(amdgpu_context_handle context_handle,
+static void _amdgpu_test_exec_cs_helper(amdgpu_context_handle context_handle,
                                       unsigned ip_type,
                                       int instance, int pm4_dw, uint32_t 
*pm4_src,
                                       int res_cnt, amdgpu_bo_handle *resources,
                                       struct amdgpu_cs_ib_info *ib_info,
-                                      struct amdgpu_cs_request *ibs_request)
+                                      struct amdgpu_cs_request *ibs_request, 
int sync, int repeat)
  {
        int r;
        uint32_t expired;
@@ -1395,12 +1398,15 @@ static void 
amdgpu_test_exec_cs_helper(amdgpu_context_handle context_handle,
        CU_ASSERT_NOT_EQUAL(ibs_request, NULL);

/* submit CS */

-       r = amdgpu_cs_submit(context_handle, 0, ibs_request, 1);
+       while (repeat--)
+               r = amdgpu_cs_submit(context_handle, 0, ibs_request, 1);
        CU_ASSERT_EQUAL(r, 0);

r = amdgpu_bo_list_destroy(ibs_request->resources);

        CU_ASSERT_EQUAL(r, 0);

+ if (!sync)

+               return;
        fence_status.ip_type = ip_type;
        fence_status.ip_instance = 0;
        fence_status.ring = ibs_request->ring;
@@ -1667,7 +1673,7 @@ static void 
amdgpu_command_submission_sdma_const_fill(void)

static void amdgpu_command_submission_copy_linear_helper(unsigned ip_type)

  {
-       const int sdma_write_length = 1024;
+       const int sdma_write_length = (255) << 20;
        const int pm4_dw = 256;
        amdgpu_context_handle context_handle;
        amdgpu_bo_handle bo1, bo2;
@@ -1715,8 +1721,6 @@ static void 
amdgpu_command_submission_copy_linear_helper(unsigned ip_type)
                                                            &bo1_va_handle);
                                CU_ASSERT_EQUAL(r, 0);

- /* set bo1 */

-                               memset((void*)bo1_cpu, 0xaa, sdma_write_length);

/* allocate UC bo2 for sDMA use */

                                r = amdgpu_bo_alloc_and_map(device_handle,
@@ -1727,8 +1731,6 @@ static void 
amdgpu_command_submission_copy_linear_helper(unsigned ip_type)
                                                            &bo2_va_handle);
                                CU_ASSERT_EQUAL(r, 0);

- /* clear bo2 */

-                               memset((void*)bo2_cpu, 0, sdma_write_length);

resources[0] = bo1;

                                resources[1] = bo2;
@@ -1785,17 +1787,11 @@ static void 
amdgpu_command_submission_copy_linear_helper(unsigned ip_type)
                                        }
                                }

- amdgpu_test_exec_cs_helper(context_handle,

+                               _amdgpu_test_exec_cs_helper(context_handle,
                                                           ip_type, ring_id,
                                                           i, pm4,
                                                           2, resources,
-                                                          ib_info, 
ibs_request);
-
-                               /* verify if SDMA test result meets with 
expected */
-                               i = 0;
-                               while(i < sdma_write_length) {
-                                       CU_ASSERT_EQUAL(bo2_cpu[i++], 0xaa);
-                               }
+                                                          ib_info, 
ibs_request, 0, 100);
                                r = amdgpu_bo_unmap_and_free(bo1, 
bo1_va_handle, bo1_mc,
                                                             sdma_write_length);
                                CU_ASSERT_EQUAL(r, 0);

Re: [PATCH v2 0/2] Fix a hung during memory pressure test

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