On Wed, Dec 23, 2015 at 01:40:06PM +0100, Christoph Mathys wrote:

On Tue, Dec 22, 2015 at 4:37 PM, Sebastian Andrzej Siewior
[off-list ref] wrote:

quoted

I have to admit, the i915 tries very hard to avoid running on -RT. Could
you try the s/local_irq_disable();/local_irq_disable_nort();/ patch
mentioned in the thread?

It did not crash so far, I did some usual work and executed glmark2
several times. The BUG has not surfaced again. BUT, the latency is
still far from ideal, it takes only seconds for the maximum latency to
spike into the range of milliseconds. By the way, this is now
4.1.15-rt17 with the changes from here:
http://www.spinics.net/lists/linux-rt-users/msg13543.html

During some tests with cyclictests --breaktrace I've seen more BUG
messages, but they might relate to the kernel tracing. Unfortunately,
I could not make much of the --breaktrace.

Waking the GT takes a while, and for a bunch of reasons we need to be able
to do this from irq context, hence spin_lock_irq. Doesn't RT convert that
to a mutex?

Otherwise not sure what would prevent interrupts in your backtrace ...
-Daniel

[ 4629.753864] BUG: sleeping function called from invalid context at
kernel/locking/rtmutex.c:917
[ 4629.753865] in_atomic(): 1, irqs_disabled(): 0, pid: 1913, name: Xorg
[ 4629.753866] 2 locks held by Xorg/1913:
[ 4629.753879]  #0:  (crtc_ww_class_acquire){+.+.+.}, at:
[<ffffffffa0211a6c>] drm_modeset_lock_crtc+0x4c/0x100 [drm]
[ 4629.753887]  #1:  (crtc_ww_class_mutex){+.+.+.}, at:
[<ffffffffa0211871>] drm_modeset_lock+0x41/0x130 [drm]
[ 4629.753888] CPU: 4 PID: 1913 Comm: Xorg Tainted: G            E
4.1.15-i915-patch-realtime-1-rt17+ #4
[ 4629.753889] Hardware name: Komax AG, Dierikon Komax-PC/KMX-B75,
BIOS DD3-1-1D 08/21/2013
[ 4629.753891]  ffffffff81c862ce ffff8803e92538b8 ffffffff81805313
0000000000005b10
[ 4629.753892]  ffff8803e8baa660 ffff8803e92538e8 ffffffff8108813a
ffff8803e92538d8
[ 4629.753893]  ffff8803fe6d0070 ffff8803fe6d0070 ffff8803fe6d0068
ffff8803e9253918
[ 4629.753893] Call Trace:
[ 4629.753897]  [<ffffffff81805313>] dump_stack+0x4a/0x61
[ 4629.753899]  [<ffffffff8108813a>] ___might_sleep+0x13a/0x200
[ 4629.753901]  [<ffffffff8180ccc4>] rt_spin_lock+0x24/0x60
[ 4629.753916]  [<ffffffffa02f61d6>] gen6_read32+0x46/0x380 [i915]
[ 4629.753925]  [<ffffffffa02d4b42>] gm45_get_vblank_counter+0x32/0x40 [i915]
[ 4629.753934]  [<ffffffffa02e11b5>]
ftrace_raw_event_i915_pipe_update_start+0x65/0xb0 [i915]
[ 4629.753944]  [<ffffffffa0324c23>] intel_pipe_update_start+0x2a3/0x640 [i915]
[ 4629.753946]  [<ffffffff810aaac0>] ? prepare_to_wait_event+0x130/0x130
[ 4629.753956]  [<ffffffffa030ffc6>] intel_begin_crtc_commit+0x166/0x1e0 [i915]
[ 4629.753961]  [<ffffffffa026e6f2>]
drm_plane_helper_commit+0x112/0x2c0 [drm_kms_helper]
[ 4629.753963]  [<ffffffffa026e93a>] drm_plane_helper_update+0x9a/0xf0
[drm_kms_helper]
[ 4629.753970]  [<ffffffffa0201bc8>] __setplane_internal+0x248/0x350 [drm]
[ 4629.753975]  [<ffffffffa0201df5>] drm_mode_cursor_universal+0x125/0x210 [drm]
[ 4629.753981]  [<ffffffffa0201f5f>] drm_mode_cursor_common+0x7f/0x1b0 [drm]
[ 4629.753987]  [<ffffffffa0206411>] drm_mode_cursor_ioctl+0x41/0x50 [drm]
[ 4629.753992]  [<ffffffffa01f60a9>] drm_ioctl+0x349/0x690 [drm]
[ 4629.753998]  [<ffffffffa02063d0>] ? drm_mode_setcrtc+0x630/0x630 [drm]
[ 4629.753999]  [<ffffffff81096585>] ? local_clock+0x25/0x30
[ 4629.754001]  [<ffffffff810b3443>] ? lock_release_holdtime.part.31+0xd3/0x1a0
[ 4629.754002]  [<ffffffff81204088>] do_vfs_ioctl+0x328/0x5e0
[ 4629.754004]  [<ffffffff812102a5>] ? __fget+0x5/0x210
[ 4629.754004]  [<ffffffff8121051a>] ? __fget_light+0x2a/0xa0
[ 4629.754005]  [<ffffffff812043c1>] SyS_ioctl+0x81/0xa0
[ 4629.754007]  [<ffffffff8180d804>] tracesys_phase2+0x88/0x8d

[  361.526236] BUG: sleeping function called from invalid context at
kernel/locking/rtmutex.c:917
[  361.526237] in_atomic(): 1, irqs_disabled(): 0, pid: 667, name: irq/51-i915
[  361.526237] no locks held by irq/51-i915/667.
[  361.526239] CPU: 4 PID: 667 Comm: irq/51-i915 Tainted: G
E   4.1.15-i915-patch-realtime-1-rt17+ #4
[  361.526240] Hardware name: Komax AG, Dierikon Komax-PC/KMX-B75,
BIOS DD3-1-1D 08/21/2013
[  361.526242]  ffffffff81c862ce ffff8803fe6e7b58 ffffffff81805313
0000000000000000
[  361.526243]  ffff8803ff3d4cc0 ffff8803fe6e7b88 ffffffff8108813a
0000000000000296
[  361.526244]  ffff8803fe6d0070 ffff8803fe6d0070 ffff8803fe6d0068
ffff8803fe6e7bb8
[  361.526244] Call Trace:
[  361.526249]  [<ffffffff81805313>] dump_stack+0x4a/0x61
[  361.526251]  [<ffffffff8108813a>] ___might_sleep+0x13a/0x200
[  361.526253]  [<ffffffff8180ccc4>] rt_spin_lock+0x24/0x60
[  361.526281]  [<ffffffffa02f61d6>] gen6_read32+0x46/0x380 [i915]
[  361.526283]  [<ffffffff81142270>] ? trace_event_buffer_lock_reserve+0x40/0x80
[  361.526293]  [<ffffffffa02e782f>] gen6_ring_get_seqno+0x2f/0x40 [i915]
[  361.526301]  [<ffffffffa02e0eef>]
ftrace_raw_event_i915_gem_request_notify+0x5f/0x90 [i915]
[  361.526309]  [<ffffffffa02d843d>] notify_ring.isra.12+0xcd/0x240 [i915]
[  361.526316]  [<ffffffffa02d8a0c>] snb_gt_irq_handler+0x12c/0x180 [i915]
[  361.526323]  [<ffffffffa02dab97>] ironlake_irq_handler+0x1c7/0xfe0 [i915]
[  361.526324]  [<ffffffff81087f0d>] ? finish_task_switch+0x4d/0x140
[  361.526325]  [<ffffffff810cf7e7>] irq_forced_thread_fn+0x27/0x70
[  361.526326]  [<ffffffff810cfd99>] irq_thread+0x149/0x1f0
[  361.526327]  [<ffffffff810cf7c0>] ? irq_thread_fn+0x40/0x40
[  361.526328]  [<ffffffff810cf860>] ? wake_threads_waitq+0x30/0x30
[  361.526329]  [<ffffffff810cfc50>] ? irq_thread_check_affinity+0x70/0x70
[  361.526330]  [<ffffffff81081854>] kthread+0xe4/0x100
[  361.526332]  [<ffffffff810b649d>] ? trace_hardirqs_on+0xd/0x10
[  361.526333]  [<ffffffff81081770>] ? kthread_create_on_node+0x240/0x240
[  361.526334]  [<ffffffff8180db22>] ret_from_fork+0x42/0x70
[  361.526335]  [<ffffffff81081770>] ? kthread_create_on_node+0x240/0x240
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch