Re: [PATCH 1/3] drm/radeon: take exclusive_lock in read mode during ring tests

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Yeah, looks like a bug.  I think the attached patch should fix it.
Sounds logical and the patch is Reviewed-by: Christian König <christian.koenig@xxxxxxx>

Going to apply Maartens patch on top and test that one a bit to make sure it works as expected.

Regards,
Christian.

Am 18.08.2014 um 18:03 schrieb Alex Deucher:
On Mon, Aug 18, 2014 at 11:02 AM, Christian König
<deathsimple@xxxxxxxxxxx> wrote:
Am 18.08.2014 um 16:45 schrieb Maarten Lankhorst:

This is needed for the next commit, because the lockup detection
will need the read lock to run.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxx>
---
   drivers/gpu/drm/radeon/radeon.h        |  2 +-
   drivers/gpu/drm/radeon/radeon_device.c | 61
++++++++++++++++++++--------------
   2 files changed, 37 insertions(+), 26 deletions(-)

diff --git a/drivers/gpu/drm/radeon/radeon.h
b/drivers/gpu/drm/radeon/radeon.h
index 9e1732eb402c..1d806983ec7b 100644
--- a/drivers/gpu/drm/radeon/radeon.h
+++ b/drivers/gpu/drm/radeon/radeon.h
@@ -2312,7 +2312,7 @@ struct radeon_device {
         bool                            need_dma32;
         bool                            accel_working;
         bool                            fastfb_working; /* IGP feature*/
-       bool                            needs_reset;
+       bool                            needs_reset, in_reset;
         struct radeon_surface_reg surface_regs[RADEON_GEM_MAX_SURFACES];
         const struct firmware *me_fw;   /* all family ME firmware */
         const struct firmware *pfp_fw;  /* r6/700 PFP firmware */
diff --git a/drivers/gpu/drm/radeon/radeon_device.c
b/drivers/gpu/drm/radeon/radeon_device.c
index c8ea050c8fa4..82633fdd399d 100644
--- a/drivers/gpu/drm/radeon/radeon_device.c
+++ b/drivers/gpu/drm/radeon/radeon_device.c
@@ -1671,29 +1671,34 @@ int radeon_gpu_reset(struct radeon_device *rdev)
         down_write(&rdev->exclusive_lock);
         if (!rdev->needs_reset) {
+               WARN_ON(rdev->in_reset);
                 up_write(&rdev->exclusive_lock);
                 return 0;
         }
         rdev->needs_reset = false;
-
-       radeon_save_bios_scratch_regs(rdev);
-       /* block TTM */
         resched = ttm_bo_lock_delayed_workqueue(&rdev->mman.bdev);
-       radeon_pm_suspend(rdev);
-       radeon_suspend(rdev);
   -     for (i = 0; i < RADEON_NUM_RINGS; ++i) {
-               ring_sizes[i] = radeon_ring_backup(rdev, &rdev->ring[i],
-                                                  &ring_data[i]);
-               if (ring_sizes[i]) {
-                       saved = true;
-                       dev_info(rdev->dev, "Saved %d dwords of commands "
-                                "on ring %d.\n", ring_sizes[i], i);
+       if (!rdev->in_reset) {
+               rdev->in_reset = true;
+
+               radeon_save_bios_scratch_regs(rdev);
+               /* block TTM */
+               radeon_pm_suspend(rdev);
+               radeon_suspend(rdev);

That won't work correctly because you might end up with calling pm_resume
more often than suspend and that can only lead to a crash. Saying this we
probably already have a bug in the reset code at this point anyway, but see
below.


+
+               for (i = 0; i < RADEON_NUM_RINGS; ++i) {
+                       ring_sizes[i] = radeon_ring_backup(rdev,
&rdev->ring[i],
+                                                          &ring_data[i]);
+                       if (ring_sizes[i]) {
+                               saved = true;
+                               dev_info(rdev->dev, "Saved %d dwords of
commands "
+                                        "on ring %d.\n", ring_sizes[i],
i);
+                       }
                 }
-       }
+       } else
+               memset(ring_data, 0, sizeof(ring_data));
   -retry:
         r = radeon_asic_reset(rdev);
         if (!r) {
                 dev_info(rdev->dev, "GPU reset succeeded, trying to
resume\n");
@@ -1702,40 +1707,46 @@ retry:
         radeon_restore_bios_scratch_regs(rdev);

We should resume PM here as well.


   -     if (!r) {
+       if (!r && saved) {
                 for (i = 0; i < RADEON_NUM_RINGS; ++i) {
                         radeon_ring_restore(rdev, &rdev->ring[i],
                                             ring_sizes[i], ring_data[i]);
-                       ring_sizes[i] = 0;
                         ring_data[i] = NULL;
                 }
+       } else {
+               radeon_fence_driver_force_completion(rdev);
+
+               for (i = 0; i < RADEON_NUM_RINGS; ++i) {
+                       kfree(ring_data[i]);
+               }
+       }
+       downgrade_write(&rdev->exclusive_lock);
+       ttm_bo_unlock_delayed_workqueue(&rdev->mman.bdev, resched);

I would unlock the delayed_workqueue first and then downgrade the readlock.


   +     if (!r) {
                 r = radeon_ib_ring_tests(rdev);
                 if (r) {
                         dev_err(rdev->dev, "ib ring test failed (%d).\n",
r);
                         if (saved) {
-                               saved = false;
+                               /* if reset fails, try without saving data
*/
+                               rdev->needs_reset = true;
                                 radeon_suspend(rdev);
-                               goto retry;
+                               up_read(&rdev->exclusive_lock);
+                               return -EAGAIN;
                         }
                 }
-       } else {
-               radeon_fence_driver_force_completion(rdev);
-               for (i = 0; i < RADEON_NUM_RINGS; ++i) {
-                       kfree(ring_data[i]);
-               }
         }


         radeon_pm_resume(rdev);

Move this more up.

Alex is more into this, but it's probably a bug in the current reset code
that this is after the IB tests, cause the IB tests needs everything powered
up and with PM handling suspended it is possible that individual blocks are
powered down.
Yeah, looks like a bug.  I think the attached patch should fix it.

Alex

Thanks,
Christian.


         drm_helper_resume_force_mode(rdev->ddev);
   -     ttm_bo_unlock_delayed_workqueue(&rdev->mman.bdev, resched);
         if (r) {
                 /* bad news, how to tell it to userspace ? */
                 dev_info(rdev->dev, "GPU reset failed\n");
         }
   -     up_write(&rdev->exclusive_lock);
+       rdev->in_reset = false;
+       up_read(&rdev->exclusive_lock);
         return r;
   }


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