Date:	Sun, 7 Oct 2012 23:00:31 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Willy Tarreau <w@....eu>
Cc:	Chris Wilson <chris@...is-wilson.co.uk>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	linux-kernel@...r.kernel.org, Dave Airlie <airlied@...il.com>
Subject: Re: 3.5 regression on i915

On Sat, Oct 06, 2012 at 10:20:16AM +0200, Willy Tarreau wrote:
> Hi Chris,
> 
> On Sat, Oct 06, 2012 at 09:04:34AM +0100, Chris Wilson wrote:
> > > The crash happens here in i915_gem_entervt_ioctl() :
> > > 
> > >     3659          BUG_ON(!list_empty(&dev_priv->mm.active_list));
> > >     3660          BUG_ON(!list_empty(&dev_priv->mm.flushing_list));
> > >  -> 3661          BUG_ON(!list_empty(&dev_priv->mm.inactive_list));
> > >     3662          mutex_unlock(&dev->struct_mutex);
> > 
> > That BUG_ON there is silly and can simply be removed. The check is to
> > verify that no batches were submitted to the kernel whilst the UMS/GEM
> > client was suspended - to which the BUG_ONs are a crude approximation.
> > Furthermore, the checks are too late, since it means we attempted to
> > program the hardware whilst it was in an invalid state, the BUG_ONs are
> > the least of your concerns at that point.
> 
> Excellent, that fixed it ! X still segfaults when KMS is used, but
> I expect more of a pure user-space issue here since there is nothing
> in dmesg.
> 
> Would some of you accept the following patch and tag it for -stable ?
> 
> Thanks,
> Willy
> 
> ---
> 
> From 3450cb7b7bd0b8fe1eab59d09e6852c4e3b22001 Mon Sep 17 00:00:00 2001
> From: Willy Tarreau <w@....eu>
> Date: Sat, 6 Oct 2012 10:09:00 +0200
> Subject: drm/i915: remove useless BUG_ON which caused a regression in 3.5.
> 
> starting an old X server causes a kernel BUG since commit 1b50247a8d:
> 
> ------------[ cut here ]------------
> kernel BUG at drivers/gpu/drm/i915/i915_gem.c:3661!
> invalid opcode: 0000 [#1] SMP
> Modules linked in: snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss uvcvideo videobuf2_core videodev videobuf2_vmalloc videobuf2_memops uhci_hcd ath9k mac80211 snd_hda_codec_realtek ath9k_common microcode ath9k_hw psmouse serio_raw sg ath cfg80211 atl1c lpc_ich mfd_core ehci_hcd snd_hda_intel snd_hda_codec snd_hwdep snd_pcm rtc_cmos snd_timer snd evdev eeepc_laptop snd_page_alloc sparse_keymap
> 
> Pid: 2866, comm: X Not tainted 3.5.6-rc1-eeepc #1 ASUSTeK Computer INC. 1005HA/1005HA
> EIP: 0060:[<c12dc291>] EFLAGS: 00013297 CPU: 0
> EIP is at i915_gem_entervt_ioctl+0xf1/0x110
> EAX: f5941df4 EBX: f5940000 ECX: 00000000 EDX: 00020000
> ESI: f5835400 EDI: 00000000 EBP: f51d7e38 ESP: f51d7e20
>  DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
> CR0: 8005003b CR2: b760e0a0 CR3: 351b6000 CR4: 000007d0
> DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
> DR6: ffff0ff0 DR7: 00000400
> Process X (pid: 2866, ti=f51d6000 task=f61af8d0 task.ti=f51d6000)
> Stack:
>  00000001 00000000 f5835414 f51d7e84 f5835400 f54f85c0 f51d7f10 c12b530b
>  00000001 c151b139 c14751b6 c152e030 00000b32 00006459 00000059 0000e200
>  00000001 00000000 00006459 c159ddd0 c12dc1a0 ffffffea 00000000 00000000
> Call Trace:
>  [<c12b530b>] drm_ioctl+0x2eb/0x440
>  [<c12dc1a0>] ? i915_gem_init+0xe0/0xe0
>  [<c1052b2b>] ? enqueue_hrtimer+0x1b/0x50
>  [<c1053321>] ? __hrtimer_start_range_ns+0x161/0x330
>  [<c10530b3>] ? lock_hrtimer_base+0x23/0x50
>  [<c1053163>] ? hrtimer_try_to_cancel+0x33/0x70
>  [<c12b5020>] ? drm_version+0x90/0x90
>  [<c10ca171>] vfs_ioctl+0x31/0x50
>  [<c10ca2e4>] do_vfs_ioctl+0x64/0x510
>  [<c10535de>] ? hrtimer_nanosleep+0x8e/0x100
>  [<c1052c20>] ? update_rmtp+0x80/0x80
>  [<c10ca7c9>] sys_ioctl+0x39/0x60
>  [<c1433949>] syscall_call+0x7/0xb
> Code: 83 c4 0c 5b 5e 5f 5d c3 c7 44 24 04 2c 05 53 c1 c7 04 24 6f ef 47 c1 e8 6e e0 fd ff c7 83 38 1e 00 00 00 00 00 00 e9 3f ff ff ff <0f> 0b eb fe 0f 0b eb fe 8d b4 26 00 00 00 00 0f 0b eb fe 8d b6
> EIP: [<c12dc291>] i915_gem_entervt_ioctl+0xf1/0x110 SS:ESP 0068:f51d7e20
> ---[ end trace dd332ec083cbd513 ]---
> 
> The crash happens here in i915_gem_entervt_ioctl() :
> 
>     3659          BUG_ON(!list_empty(&dev_priv->mm.active_list));
>     3660          BUG_ON(!list_empty(&dev_priv->mm.flushing_list));
>  -> 3661          BUG_ON(!list_empty(&dev_priv->mm.inactive_list));
>     3662          mutex_unlock(&dev->struct_mutex);
> 
> Quoting Chris :
>   "That BUG_ON there is silly and can simply be removed. The check is to
>    verify that no batches were submitted to the kernel whilst the UMS/GEM
>    client was suspended - to which the BUG_ONs are a crude approximation.
>    Furthermore, the checks are too late, since it means we attempted to
>    program the hardware whilst it was in an invalid state, the BUG_ONs are
>    the least of your concerns at that point."
> 
> Cc: Chris Wilson <chris@...is-wilson.co.uk>
> Signed-off-by: Willy Tarreau <w@....eu>

Applied to -fixes, with cc: stable and a note mentioning the regressing
commit sha1 added.

Thanks, Daniel
> ---
>  drivers/gpu/drm/i915/i915_gem.c |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 35926ad..fc6683a 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3658,7 +3658,6 @@ i915_gem_entervt_ioctl(struct drm_device *dev, void *data,
>  
>  	BUG_ON(!list_empty(&dev_priv->mm.active_list));
>  	BUG_ON(!list_empty(&dev_priv->mm.flushing_list));
> -	BUG_ON(!list_empty(&dev_priv->mm.inactive_list));
>  	mutex_unlock(&dev->struct_mutex);
>  
>  	ret = drm_irq_install(dev);
> -- 
> 1.7.2.1.45.g54fbc
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
--
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