On Tue, 6 Aug 2019 21:00:10 +0300 From: Jaak Ristioja jaak@ristioja.ee

...

Hello!

I'm writing to report a crash in the QXL / DRM code in the Linux kernel. I originally filed the issue on LaunchPad and more details can be found there, although I doubt whether these details are useful.

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1813620

I first experienced these issues with:

• Ubuntu 18.04 (probably kernel 4.15.something)
• Ubuntu 18.10 (kernel 4.18.0-13)
• Ubuntu 19.04 (kernel 5.0.0-13-generic)
• Ubuntu 19.04 (mainline kernel 5.1-rc7)
• Ubuntu 19.04 (mainline kernel 5.2.0-050200rc1-generic)

Here is the crash output from dmesg:

[354073.713350] INFO: task Xorg:920 blocked for more than 120 seconds. [354073.717755] Not tainted 5.2.0-050200rc1-generic #201905191930 [354073.722277] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [354073.738332] Xorg D 0 920 854 0x00404004 [354073.738334] Call Trace: [354073.738340] __schedule+0x2ba/0x650 [354073.738342] schedule+0x2d/0x90 [354073.738343] schedule_preempt_disabled+0xe/0x10 [354073.738345] __ww_mutex_lock.isra.11+0x3e0/0x750 [354073.738346] __ww_mutex_lock_slowpath+0x16/0x20 [354073.738347] ww_mutex_lock+0x34/0x50 [354073.738352] ttm_eu_reserve_buffers+0x1f9/0x2e0 [ttm] [354073.738356] qxl_release_reserve_list+0x67/0x150 [qxl] [354073.738358] ? qxl_bo_pin+0xaa/0x190 [qxl] [354073.738359] qxl_cursor_atomic_update+0x1b0/0x2e0 [qxl] [354073.738367] drm_atomic_helper_commit_planes+0xb9/0x220 [drm_kms_helper] [354073.738371] drm_atomic_helper_commit_tail+0x2b/0x70 [drm_kms_helper] [354073.738374] commit_tail+0x67/0x70 [drm_kms_helper] [354073.738378] drm_atomic_helper_commit+0x113/0x120 [drm_kms_helper] [354073.738390] drm_atomic_commit+0x4a/0x50 [drm] [354073.738394] drm_atomic_helper_update_plane+0xe9/0x100 [drm_kms_helper] [354073.738402] __setplane_atomic+0xd3/0x120 [drm] [354073.738410] drm_mode_cursor_universal+0x142/0x270 [drm] [354073.738418] drm_mode_cursor_common+0xcb/0x220 [drm] [354073.738425] ? drm_mode_cursor_ioctl+0x60/0x60 [drm] [354073.738432] drm_mode_cursor2_ioctl+0xe/0x10 [drm] [354073.738438] drm_ioctl_kernel+0xb0/0x100 [drm] [354073.738440] ? ___sys_recvmsg+0x16c/0x200 [354073.738445] drm_ioctl+0x233/0x410 [drm] [354073.738452] ? drm_mode_cursor_ioctl+0x60/0x60 [drm] [354073.738454] ? timerqueue_add+0x57/0x90 [354073.738456] ? enqueue_hrtimer+0x3c/0x90 [354073.738458] do_vfs_ioctl+0xa9/0x640 [354073.738459] ? fput+0x13/0x20 [354073.738461] ? __sys_recvmsg+0x88/0xa0 [354073.738462] ksys_ioctl+0x67/0x90 [354073.738463] __x64_sys_ioctl+0x1a/0x20 [354073.738465] do_syscall_64+0x5a/0x140 [354073.738467] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [354073.738468] RIP: 0033:0x7ffad14d3417 [354073.738472] Code: Bad RIP value. [354073.738472] RSP: 002b:00007ffdd5679978 EFLAGS: 00003246 ORIG_RAX: 0000000000000010 [354073.738473] RAX: ffffffffffffffda RBX: 000056428a474610 RCX: 00007ffad14d3417 [354073.738474] RDX: 00007ffdd56799b0 RSI: 00000000c02464bb RDI: 000000000000000e [354073.738474] RBP: 00007ffdd56799b0 R08: 0000000000000040 R09: 0000000000000010 [354073.738475] R10: 000000000000003f R11: 0000000000003246 R12: 00000000c02464bb [354073.738475] R13: 000000000000000e R14: 0000000000000000 R15: 000056428a4721d0 [354073.738511] INFO: task kworker/1:0:27625 blocked for more than 120 seconds. [354073.745154] Not tainted 5.2.0-050200rc1-generic #201905191930 [354073.751900] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [354073.762197] kworker/1:0 D 0 27625 2 0x80004000 [354073.762205] Workqueue: events qxl_client_monitors_config_work_func [qxl] [354073.762206] Call Trace: [354073.762211] __schedule+0x2ba/0x650 [354073.762214] schedule+0x2d/0x90 [354073.762215] schedule_preempt_disabled+0xe/0x10 [354073.762216] __ww_mutex_lock.isra.11+0x3e0/0x750 [354073.762217] ? __switch_to_asm+0x34/0x70 [354073.762218] ? __switch_to_asm+0x40/0x70 [354073.762219] ? __switch_to_asm+0x40/0x70 [354073.762220] __ww_mutex_lock_slowpath+0x16/0x20 [354073.762221] ww_mutex_lock+0x34/0x50 [354073.762235] drm_modeset_lock+0x35/0xb0 [drm] [354073.762243] drm_modeset_lock_all_ctx+0x5d/0xe0 [drm] [354073.762251] drm_modeset_lock_all+0x5e/0xb0 [drm] [354073.762252] qxl_display_read_client_monitors_config+0x1e1/0x370 [qxl] [354073.762254] qxl_client_monitors_config_work_func+0x15/0x20 [qxl] [354073.762256] process_one_work+0x20f/0x410 [354073.762257] worker_thread+0x34/0x400 [354073.762259] kthread+0x120/0x140 [354073.762260] ? process_one_work+0x410/0x410 [354073.762261] ? __kthread_parkme+0x70/0x70 [354073.762262] ret_from_fork+0x35/0x40

--- a/drivers/gpu/drm/ttm/ttm_execbuf_util.c +++ b/drivers/gpu/drm/ttm/ttm_execbuf_util.c @@ -97,8 +97,9 @@ int ttm_eu_reserve_buffers(struct ww_acq struct list_head *dups, bool del_lru) { struct ttm_bo_global *glob;

• struct ttm_validate_buffer *entry;

• struct ttm_validate_buffer *entry, *last_entry; int ret;

• bool locked = false;

  if (list_empty(list)) return 0;

@@ -112,7 +113,10 @@ int ttm_eu_reserve_buffers(struct ww_acq list_for_each_entry(entry, list, head) { struct ttm_buffer_object *bo = entry->bo;

• last_entry = entry;
  

  ret = __ttm_bo_reserve(bo, intr, (ticket == NULL), ticket);

• if (!ret)
  

• 	locked = true;
  

  if (!ret && unlikely(atomic_read(&bo->cpu_writers) > 0)) { reservation_object_unlock(bo->resv);

@@ -151,6 +155,10 @@ int ttm_eu_reserve_buffers(struct ww_acq ret = 0; } }

• if (!ret)
  

• 	locked = true;
  

• else
  

• 	locked = false;
  
  

locked = !ret;

?

if (!ret && entry->num_shared)
	ret = reservation_object_reserve_shared(bo->resv,

@@ -163,6 +171,8 @@ int ttm_eu_reserve_buffers(struct ww_acq ww_acquire_done(ticket); ww_acquire_fini(ticket); }

• 	if (locked)
  

• 		ttm_eu_backoff_reservation_reverse(list, entry);
  return ret;
  

  }

@@ -172,6 +182,8 @@ int ttm_eu_reserve_buffers(struct ww_acq list_del(&entry->head); list_add(&entry->head, list); }

• if (locked)

• ttm_eu_backoff_reservation_reverse(list, last_entry);
  
  

  if (del_lru) { spin_lock(&glob->lru_lock);

Where does it came this patch? Is it already somewhere? Is it supposed to fix this issue? Does it affect some other card beside QXL?

Frediano

Hi,

--verbose please. Do you see the same hang? Does the patch fix it?

--- a/drivers/gpu/drm/ttm/ttm_execbuf_util.c +++ b/drivers/gpu/drm/ttm/ttm_execbuf_util.c @@ -97,8 +97,9 @@ int ttm_eu_reserve_buffers(struct ww_acq struct list_head *dups, bool del_lru)

[ ... ]

• 	if (locked)
  

• 		ttm_eu_backoff_reservation_reverse(list, entry);
  

Hmm, I think the patch is wrong. As far I know it is the qxl drivers's job to call ttm_eu_backoff_reservation(). Doing that automatically in ttm will most likely break other ttm users.

So I guess the call is missing in the qxl driver somewhere, most likely in some error handling code path given that this bug is a relatively rare event.

There is only a single ttm_eu_reserve_buffers() call in qxl. So how about this?

----------------------- cut here -------------------- diff --git a/drivers/gpu/drm/qxl/qxl_release.c b/drivers/gpu/drm/qxl/qxl_release.c index 312216caeea2..2f9950fa0b8d 100644 --- a/drivers/gpu/drm/qxl/qxl_release.c +++ b/drivers/gpu/drm/qxl/qxl_release.c @@ -262,18 +262,20 @@ int qxl_release_reserve_list(struct qxl_release *release, bool no_intr) ret = ttm_eu_reserve_buffers(&release->ticket, &release->bos, !no_intr, NULL, true); if (ret) - return ret; + goto err_backoff;

list_for_each_entry(entry, &release->bos, tv.head) { struct qxl_bo *bo = to_qxl_bo(entry->tv.bo);

ret = qxl_release_validate_bo(bo); - if (ret) { - ttm_eu_backoff_reservation(&release->ticket, &release->bos); - return ret; - } + if (ret) + goto err_backoff; } return 0; + +err_backoff: + ttm_eu_backoff_reservation(&release->ticket, &release->bos); + return ret; }

void qxl_release_backoff_reserve_list(struct qxl_release *release) ----------------------- cut here --------------------

cheers, Gerd