Re: [REGRESSION 4.12] i915 Oops at intel_fbdev_invalidate()

[Chris Wilson]

Quoting Takashi Iwai (2017-06-30 16:38:46)
> Hi,
> 
> I hit an Oops with the latest Linus tree (4.12-rc7+) on a HSW machine
> like the following at boot:
> 
>  BUG: unable to handle kernel NULL pointer dereference at 00000000000000b0
>  IP: intel_fbdev_invalidate.isra.3+0xc/0x40 [i915]
>  Oops: 0000 [#1] PREEMPT SMP
>  CPU: 2 PID: 833 Comm: X Not tainted 4.10.0-rc5-btest9+ #15
>  Hardware name: Hewlett-Packard HP ProBook 430 G1/1946, BIOS L73 Ver. 08.05 2013/03/15
>  task: ffff917313db8000 task.stack: ffffb6e70379c000
>  RIP: 0010:intel_fbdev_invalidate.isra.3+0xc/0x40 [i915]
>  RSP: 0018:ffffb6e70379fde0 EFLAGS: 00010246
>  RAX: 0000000000000000 RBX: ffff9172f70e1c00 RCX: 0000000000000000
>  RDX: ffff917313db8000 RSI: 0000000000000000 RDI: ffff91731934d040
>  RBP: ffffb6e70379fdf0 R08: 0000000000000002 R09: ffff91731934ead0
>  R10: ffff9173192f0368 R11: 0000000000000001 R12: ffff9173192f0000
>  R13: ffff9172f71016e8 R14: ffff9173227c8480 R15: ffff9172f71016c8
>  FS:  00007f8cc8c3fa00(0000) GS:ffff9173c0a80000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 00000000000000b0 CR3: 000000006273b000 CR4: 00000000001406e0
>  Call Trace:
>   ? intel_fbdev_restore_mode+0x4e/0x70 [i915]
>   i915_driver_lastclose+0xe/0x20 [i915]
>   drm_lastclose+0x3b/0xf0 [drm]
>   drm_release+0x2b8/0x360 [drm]
>   __fput+0xd9/0x1e0
>   ____fput+0xe/0x10
>   task_work_run+0x83/0xa0
>   exit_to_usermode_loop+0x59/0x85
>   do_syscall_64+0xb3/0xd0
>   entry_SYSCALL64_slow_path+0x25/0x25
> 
> And git bisection leaded to the commit 
> fabef825626d7bd05a321e4427fdf31a169b5173
>     drm/i915: Drop struct_mutex around frontbuffer flushes
> 
> The band-aid patch below seems fixing it.

See https://patchwork.freedesktop.org/patch/163261/
-Chris