Re: [PATCH v2] drm/sched: Fix kernel NULL pointer dereference error

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On 10/12/2022 7:05 PM, Christian König wrote:
That essentially looks like the right approach, but I would go a few steps further.

I think we should add a drm_sched_fence_set_parent() function to sched_fence.c and move a good part of the handling into that C file. Just a simple signal function which tells the scheduler that it should decrement it's counter and wake up the main thread.

I have added these two functions in sched_fence.c . Here, I have used drm_sched_job_done() function as it is.

Is that fine?

void drm_sched_fence_add_parent_cb(struct dma_fence *fence,
                                   struct drm_sched_fence *s_fence)
{
        int r = dma_fence_add_callback(fence, &s_fence->cb,
                                       drm_sched_job_done_cb);
        if (r == -ENOENT)
                drm_sched_job_done(s_fence);
        else if (r)
                DRM_ERROR("fence add callback failed (%d)\n", r);
}

bool drm_sched_fence_remove_parent_cb(struct drm_sched_fence *s_fence) {
        return dma_fence_remove_callback(s_fence->parent,
                                         &s_fence->cb);
}

Thanks

~Arvind

Regards,
Christian.

Am 12.10.22 um 15:22 schrieb Arvind Yadav:
This is purely a timing issue. Here, sometimes Job free
is happening before the job is done.
To fix this issue moving 'dma_fence_cb' callback from
job(struct drm_sched_job) to scheduler fence (struct drm_sched_fence).

BUG: kernel NULL pointer dereference, address: 0000000000000088
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 0 P4D 0
  Oops: 0000 [#1] PREEMPT SMP NOPTI
  CPU: 2 PID: 0 Comm: swapper/2 Not tainted 6.0.0-rc2-custom #1
  Arvind : [dma_fence_default_wait _START] timeout = -1
  Hardware name: AMD Dibbler/Dibbler, BIOS RDB1107CC 09/26/2018
  RIP: 0010:drm_sched_job_done.isra.0+0x11/0x140 [gpu_sched]
  Code: 8b fe ff ff be 03 00 00 00 e8 7b da b7 e3 e9 d4 fe ff ff 66 0f 1f 44 00 00 0f 1f 44 00 00 55 48 89 e5 41 55 41 54 49 89 fc 53 <48> 8b 9f 88 00 00 00 f0 ff 8b f0 00 00 00 48 8b 83 80 01 00 00 f0
  RSP: 0018:ffffb1b1801d4d38 EFLAGS: 00010087
  RAX: ffffffffc0aa48b0 RBX: ffffb1b1801d4d70 RCX: 0000000000000018
  RDX: 000036c70afb7c1d RSI: ffff8a45ca413c60 RDI: 0000000000000000
  RBP: ffffb1b1801d4d50 R08: 00000000000000b5 R09: 0000000000000000
  R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
  R13: ffffb1b1801d4d70 R14: ffff8a45c4160000 R15: ffff8a45c416a708
  FS:  0000000000000000(0000) GS:ffff8a48a0a80000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000088 CR3: 000000014ad50000 CR4: 00000000003506e0
  Call Trace:
   <IRQ>
   drm_sched_job_done_cb+0x12/0x20 [gpu_sched]
   dma_fence_signal_timestamp_locked+0x7e/0x110
   dma_fence_signal+0x31/0x60
   amdgpu_fence_process+0xc4/0x140 [amdgpu]
   gfx_v9_0_eop_irq+0x9d/0xd0 [amdgpu]
   amdgpu_irq_dispatch+0xb7/0x210 [amdgpu]
   amdgpu_ih_process+0x86/0x100 [amdgpu]
   amdgpu_irq_handler+0x24/0x60 [amdgpu]
   __handle_irq_event_percpu+0x4b/0x190
   handle_irq_event_percpu+0x15/0x50
   handle_irq_event+0x39/0x60
   handle_edge_irq+0xaf/0x210
   __common_interrupt+0x6e/0x110
   common_interrupt+0xc1/0xe0
   </IRQ>
   <TASK>

Signed-off-by: Arvind Yadav <Arvind.Yadav@xxxxxxx>
---

Changes in v2: Moving 'dma_fence_cb' callback from
job(struct drm_sched_job) to scheduler fence(struct drm_sched_fence)
instead of adding NULL check for s_fence.

---
  drivers/gpu/drm/scheduler/sched_main.c | 23 +++++++++++------------
  include/drm/gpu_scheduler.h            |  6 ++++--
  2 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 4cc59bae38dd..62d8eca05b92 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -253,13 +253,12 @@ drm_sched_rq_select_entity_fifo(struct drm_sched_rq *rq)
    /**
   * drm_sched_job_done - complete a job
- * @s_job: pointer to the job which is done
+ * @s_fence: pointer to the fence of a done job
   *
   * Finish the job's fence and wake up the worker thread.
   */
-static void drm_sched_job_done(struct drm_sched_job *s_job)
+static void drm_sched_job_done(struct drm_sched_fence *s_fence)
  {
-    struct drm_sched_fence *s_fence = s_job->s_fence;
      struct drm_gpu_scheduler *sched = s_fence->sched;
        atomic_dec(&sched->hw_rq_count);
@@ -280,9 +279,9 @@ static void drm_sched_job_done(struct drm_sched_job *s_job)
   */
  static void drm_sched_job_done_cb(struct dma_fence *f, struct dma_fence_cb *cb)
  {
-    struct drm_sched_job *s_job = container_of(cb, struct drm_sched_job, cb); +    struct drm_sched_fence *s_fence = container_of(cb, struct drm_sched_fence, cb);
  -    drm_sched_job_done(s_job);
+    drm_sched_job_done(s_fence);
  }
    /**
@@ -506,7 +505,7 @@ void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
                       list) {
          if (s_job->s_fence->parent &&
dma_fence_remove_callback(s_job->s_fence->parent,
-                          &s_job->cb)) {
+                          &s_job->s_fence->cb)) {
              dma_fence_put(s_job->s_fence->parent);
              s_job->s_fence->parent = NULL;
              atomic_dec(&sched->hw_rq_count);
@@ -576,15 +575,15 @@ void drm_sched_start(struct drm_gpu_scheduler *sched, bool full_recovery)
              continue;
            if (fence) {
-            r = dma_fence_add_callback(fence, &s_job->cb,
+            r = dma_fence_add_callback(fence, &s_job->s_fence->cb,
                             drm_sched_job_done_cb);
              if (r == -ENOENT)
-                drm_sched_job_done(s_job);
+                drm_sched_job_done(s_job->s_fence);
              else if (r)
                  DRM_DEV_ERROR(sched->dev, "fence add callback failed (%d)\n",
                        r);
          } else
-            drm_sched_job_done(s_job);
+            drm_sched_job_done(s_job->s_fence);
      }
        if (full_recovery) {
@@ -1053,10 +1052,10 @@ static int drm_sched_main(void *param)
              /* Drop for original kref_init of the fence */
              dma_fence_put(fence);
  -            r = dma_fence_add_callback(fence, &sched_job->cb,
+            r = dma_fence_add_callback(fence, &s_fence->cb,
                             drm_sched_job_done_cb);
              if (r == -ENOENT)
-                drm_sched_job_done(sched_job);
+                drm_sched_job_done(s_fence);
              else if (r)
                  DRM_DEV_ERROR(sched->dev, "fence add callback failed (%d)\n",
                        r);
@@ -1064,7 +1063,7 @@ static int drm_sched_main(void *param)
              if (IS_ERR(fence))
                  dma_fence_set_error(&s_fence->finished, PTR_ERR(fence));
  -            drm_sched_job_done(sched_job);
+            drm_sched_job_done(s_fence);
          }
            wake_up(&sched->job_scheduled);
diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
index 1f7d9dd1a444..9a96d49dfd75 100644
--- a/include/drm/gpu_scheduler.h
+++ b/include/drm/gpu_scheduler.h
@@ -281,6 +281,10 @@ struct drm_sched_fence {
           * @owner: job owner for debugging
           */
      void                *owner;
+    /**
+     * @cb: callback
+     */
+    struct dma_fence_cb cb;
  };
    struct drm_sched_fence *to_drm_sched_fence(struct dma_fence *f);
@@ -300,7 +304,6 @@ struct drm_sched_fence *to_drm_sched_fence(struct dma_fence *f);
   *         be scheduled further.
   * @s_priority: the priority of the job.
   * @entity: the entity to which this job belongs.
- * @cb: the callback for the parent fence in s_fence.
   *
   * A job is created by the driver using drm_sched_job_init(), and
   * should call drm_sched_entity_push_job() once it wants the scheduler
@@ -325,7 +328,6 @@ struct drm_sched_job {
      atomic_t            karma;
      enum drm_sched_priority        s_priority;
      struct drm_sched_entity         *entity;
-    struct dma_fence_cb        cb;
      /**
       * @dependencies:
       *




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