If you try to reset a GPU using=20
cat /sys/kernel/debug/dri/2/amdgpu_gpu_recovery
while the GPU is hung the kernel deadlocks if the GPU is used for displaying
stuff.
I found two causes. If I hang the GPU with the libdrm tests I get a deadloc=
k in
https://cgit.freedesktop.org/~agd5f/linux/tree=
/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c?h=3Damd-staging-drm-next&id=3Dd=
a603c1d0aac505485490f5e0ba495d4e292e7b9#n1876
Looks like we disable DC during the reset, but as part of the disabling we
change the clocks and for that we wait till the GPU is idle. It is of course
not going to be idle without intervention if hung.
Supporting trace:
[ 1842.823262] INFO: task cat:3635 blocked for more than 120 seconds.
[ 1842.823268] Tainted: G W 4.16.0-rc7-g36031c0dfb2d #6
[ 1842.823270] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs&qu=
ot; disables this
message.
[ 1842.823271] cat D 0 3635 3630 0x00000000
[ 1842.823275] Call Trace:
[ 1842.823285] ? __schedule+0x23c/0x870
[ 1842.823288] schedule+0x2f/0x90
[ 1842.823291] schedule_timeout+0x1fc/0x460
[ 1842.823296] ? __alloc_pages_nodemask+0x10f/0xfd0
[ 1842.823300] dma_fence_default_wait+0x1eb/0x280
[ 1842.823303] ? dma_fence_default_wait+0x280/0x280
[ 1842.823306] dma_fence_wait_timeout+0x38/0x110
[ 1842.823331] amdgpu_fence_wait_empty+0x98/0xd0 [amdgpu]
[ 1842.823356] ? dc_remove_plane_from_context+0x202/0x240 [amdgpu]
[ 1842.823378] amdgpu_pm_compute_clocks.part.8+0x70/0x590 [amdgpu]
[ 1842.823409] dm_pp_apply_display_requirements+0x159/0x160 [amdgpu]
[ 1842.823433] pplib_apply_display_requirements+0x197/0x1c0 [amdgpu]
[ 1842.823457] dc_commit_state+0x23b/0x560 [amdgpu]
[ 1842.823481] ? dce112_validate_bandwidth+0x1bd/0x230 [amdgpu]
[ 1842.823506] ? dce112_validate_bandwidth+0x1c9/0x230 [amdgpu]
[ 1842.823535] amdgpu_dm_atomic_commit_tail+0x27a/0xc70 [amdgpu]
[ 1842.823540] ? __wake_up_common_lock+0x89/0xc0
[ 1842.823542] ? wait_for_common+0x151/0x180
[ 1842.823545] ? wait_for_common+0x151/0x180
[ 1842.823551] commit_tail+0x3d/0x70 [drm_kms_helper]
[ 1842.823557] drm_atomic_helper_commit+0xfc/0x110 [drm_kms_helper]
[ 1842.823562] drm_atomic_helper_disable_all+0x158/0x1b0 [drm_kms_helper]
[ 1842.823567] drm_atomic_helper_suspend+0xd6/0x130 [drm_kms_helper]
[ 1842.823587] amdgpu_device_gpu_recover+0x60f/0x8b0 [amdgpu]
[ 1842.823591] ? __kmalloc_node+0x204/0x2b0
[ 1842.823611] amdgpu_debugfs_gpu_recover+0x30/0x40 [amdgpu]
[ 1842.823615] seq_read+0xee/0x480
[ 1842.823619] full_proxy_read+0x53/0x80
[ 1842.823624] __vfs_read+0x36/0x150
[ 1842.823627] vfs_read+0x91/0x130
[ 1842.823630] SyS_read+0x52/0xc0
[ 1842.823634] do_syscall_64+0x67/0x120
[ 1842.823637] entry_SYSCALL_64_after_hwframe+0x3d/0xa2
[ 1842.823640] RIP: 0033:0x7f987c073701
[ 1842.823642] RSP: 002b:00007ffc0deeac08 EFLAGS: 00000246 ORIG_RAX:
0000000000000000
[ 1842.823644] RAX: ffffffffffffffda RBX: 0000000000020000 RCX:
00007f987c073701
[ 1842.823646] RDX: 0000000000020000 RSI: 00007f987c549000 RDI:
0000000000000003
[ 1842.823647] RBP: 0000000000020000 R08: 00000000ffffffff R09:
0000000000000000
[ 1842.823649] R10: 0000000000000022 R11: 0000000000000246 R12:
00007f987c549000
[ 1842.823650] R13: 0000000000000003 R14: 00007f987c54900f R15:
0000000000020000
I managed to "fix" this by commenting out that code. Now a libdrm=
test caused
hang recovers successfully though the display (even for the non-X terminals=
) is
garbled.
However, I recently had a game hang and then tried recovering and that still
gave a deadlock:
[127426.165215] INFO: task kworker/u256:0:77605 blocked for more than 120
seconds.
[127426.165221] Tainted: G W 4.16.0-rc7-gffd4abe7dbf9 #7
[127426.165222] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs&q=
uot; disables
this message.
[127426.165224] kworker/u256:0 D 0 77605 2 0x80000000
[127426.165236] Workqueue: events_unbound commit_work [drm_kms_helper]
[127426.165239] Call Trace:
[127426.165248] ? __schedule+0x23c/0x870
[127426.165251] schedule+0x2f/0x90
[127426.165254] schedule_timeout+0x1fc/0x460
[127426.165283] ? dce120_timing_generator_get_crtc_position+0x5b/0x70 [amd=
gpu]
[127426.165308] ? dce120_timing_generator_get_crtc_scanoutpos+0x70/0xb0
[amdgpu]
[127426.165312] dma_fence_default_wait+0x1eb/0x280
[127426.165315] ? dma_fence_default_wait+0x280/0x280
[127426.165317] dma_fence_wait_timeout+0x38/0x110
[127426.165320] reservation_object_wait_timeout_rcu+0x187/0x360
[127426.165350] amdgpu_dm_do_flip+0x109/0x350 [amdgpu]
[127426.165382] amdgpu_dm_atomic_commit_tail+0xa7c/0xc70 [amdgpu]
[127426.165386] ? wait_for_common+0x151/0x180
[127426.165390] ? pick_next_task_fair+0x48c/0x5a0
[127426.165393] ? __switch_to+0x199/0x460
[127426.165399] commit_tail+0x3d/0x70 [drm_kms_helper]
[127426.165403] process_one_work+0x1ce/0x3f0
[127426.165405] worker_thread+0x2b/0x3d0
[127426.165408] ? process_one_work+0x3f0/0x3f0
[127426.165410] kthread+0x113/0x130
[127426.165413] ? kthread_create_on_node+0x70/0x70
[127426.165416] ret_from_fork+0x22/0x40
which seems to be here:
https://cgit.freedesktop.org/~agd5f=
/linux/tree/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c?h=3Damd-stagi=
ng-drm-next&id=3Dda603c1d0aac505485490f5e0ba495d4e292e7b9#n3973
This is before the GPU reset itself happens, so either we use a BO somehow =
in
the disabled state or this is an earlier flip.
Anyway that wait is not going to finish due to a hung GPU.