RE: [PATCH] drm/amdgpu: Fix the dead lock issue.

["Deng, Emily" <Emily.Deng-5C7GfCeVMHo@public.gmane.org>]

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From: Christian König <ckoenig.leichtzumerken@gmail.com>
Sent: Tuesday, September 11, 2018 2:40 PM
To: Zhou, David(ChunMing) <David1.Zhou@amd.com>; Deng, Emily <Emily.Deng@amd.com>; Zhou, David(ChunMing) <David1.Zhou@amd.com>; amd-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/amdgpu: Fix the dead lock issue.

That won't work correctly. The TTM BO is unreferenced in a couple of more places which we don't have control over.

To make it even worse we actually can't take the reservation lock during GPU reset because the reservation object might already be destroyed when we remove the BO from the list.

I will take a look at this myself today to find a solution which should work.
Ok, thanks very much.

Best wishes
Emily Deng




Regards,
Christian.

Am 11.09.2018 um 07:41 schrieb zhoucm1:


On 2018年09月11日 11:37, zhoucm1 wrote:



On 2018年09月11日 11:32, Deng, Emily wrote:

-----Original Message-----
From: amd-gfx <amd-gfx-bounces@lists.freedesktop.org><mailto:amd-gfx-bounces@lists.freedesktop.org> On Behalf Of
zhoucm1
Sent: Tuesday, September 11, 2018 11:28 AM
To: Deng, Emily <Emily.Deng@amd.com><mailto:Emily.Deng@amd.com>; Zhou, David(ChunMing)
<David1.Zhou@amd.com><mailto:David1.Zhou@amd.com>; amd-gfx@lists.freedesktop.org<mailto:amd-gfx@lists.freedesktop.org>
Subject: Re: [PATCH] drm/amdgpu: Fix the dead lock issue.



On 2018年09月11日 11:23, Deng, Emily wrote:

-----Original Message-----
From: Zhou, David(ChunMing)
Sent: Tuesday, September 11, 2018 11:03 AM
To: Deng, Emily <Emily.Deng@amd.com><mailto:Emily.Deng@amd.com>; amd-gfx@lists.freedesktop.org<mailto:amd-gfx@lists.freedesktop.org>
Subject: Re: [PATCH] drm/amdgpu: Fix the dead lock issue.



On 2018年09月11日 10:51, Emily Deng wrote:

It will ramdomly have the dead lock issue when test TDR:
1. amdgpu_device_handle_vram_lost gets the lock shadow_list_lock 2.
amdgpu_bo_create locked the bo's resv lock 3.
amdgpu_bo_create_shadow is waiting for the shadow_list_lock 4.
amdgpu_device_recover_vram_from_shadow is waiting for the bo's resv
lock.

v2:
      Make a local copy of the list

Signed-off-by: Emily Deng <Emily.Deng@amd.com><mailto:Emily.Deng@amd.com>
---
    drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 21
++++++++++++++++++++-

    1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index 2a21267..8c81404 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -3105,6 +3105,9 @@ static int
amdgpu_device_handle_vram_lost(struct amdgpu_device *adev)

        long r = 1;
        int i = 0;
        long tmo;
+    struct list_head local_shadow_list;
+
+    INIT_LIST_HEAD(&local_shadow_list);

        if (amdgpu_sriov_runtime(adev))
            tmo = msecs_to_jiffies(8000);
@@ -3112,8 +3115,19 @@ static int
amdgpu_device_handle_vram_lost(struct amdgpu_device *adev)

            tmo = msecs_to_jiffies(100);

        DRM_INFO("recover vram bo from shadow start\n");
+
+    mutex_lock(&adev->shadow_list_lock);
+    list_splice_init(&adev->shadow_list, &local_shadow_list);
+    mutex_unlock(&adev->shadow_list_lock);
+
+
        mutex_lock(&adev->shadow_list_lock);
local_shadow_list is a local variable, I think it doesn't need lock
at all, no one change it. Otherwise looks good to me.
The bo->shadow_list which now is in local_shadow_list maybe destroy in
case that it already in amdgpu_bo_destroy, then it will change
local_shadow_list, so need lock the shadow_list_lock.
Ah, sorry for noise, I forget you don't reference these BOs.
Yes, I don't reference these Bos, as I found even reference these Bos, it still couldn't avoid the case that another process is already
in amdgpu_bo_destroy.
??? that shouldn't happen, the reference is belonged to list. But back to here, we don't need reference them.
And since no shadow BO is added to local after splice, we'd better to use list_next_entry to iterate the local shadow list instead of list_for_each_entry_safe.

Thanks,
David Zhou

Thanks,
David Zhou

Best wishes
Emily Deng

Thanks,
David Zhou

-    list_for_each_entry_safe(bo, tmp, &adev->shadow_list, shadow_list) {
+    list_for_each_entry_safe(bo, tmp, &local_shadow_list, shadow_list) {
because shadow list doesn't take bo reference, we should give a amdgpu_bo_ref(bo) with attached patch before unlock.
You can have a try.

Thanks,
David Zhou

+ mutex_unlock(&adev->shadow_list_lock);
+
+        if (!bo)
+            continue;
+
            next = NULL;
            amdgpu_device_recover_vram_from_shadow(adev, ring, bo,
&next);

            if (fence) {
@@ -3132,9 +3146,14 @@ static int
amdgpu_device_handle_vram_lost(struct amdgpu_device *adev)

            dma_fence_put(fence);
            fence = next;
+        mutex_lock(&adev->shadow_list_lock);
        }
        mutex_unlock(&adev->shadow_list_lock);

+    mutex_lock(&adev->shadow_list_lock);
+    list_splice_init(&local_shadow_list, &adev->shadow_list);
+    mutex_unlock(&adev->shadow_list_lock);
+
        if (fence) {
            r = dma_fence_wait_timeout(fence, false, tmo);
            if (r == 0)
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