Date:	Wed, 30 Mar 2016 11:54:34 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Bjørn Mork <bjorn@...k.no>
Cc:	Daniel Vetter <daniel.vetter@...el.com>,
	David Airlie <airlied@...ux.ie>,
	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH] drm/i915: fix deadlock on lid open

On Wed, Mar 30, 2016 at 11:08:33AM +0200, Bjørn Mork wrote:
> commit e2c8b8701e2d moved modeset locking inside resume/suspend
> functions, but missed a code path only executed on lid close/open
> on older hardware. The result was a deadlock when closing and
> opening the lid without suspending on such hardware:
> 
>  =============================================
>  [ INFO: possible recursive locking detected ]
>  4.6.0-rc1 #385 Not tainted
>  ---------------------------------------------
>  kworker/0:3/88 is trying to acquire lock:
>   (&dev->mode_config.mutex){+.+.+.}, at: [<ffffffffa063e6a4>] intel_display_resume+0x4a/0x12f [i915]
> 
>  but task is already holding lock:
>   (&dev->mode_config.mutex){+.+.+.}, at: [<ffffffffa02d0d4f>] drm_modeset_lock_all+0x3e/0xa6 [drm]
> 
>  other info that might help us debug this:
>   Possible unsafe locking scenario:
> 
>         CPU0
>         ----
>    lock(&dev->mode_config.mutex);
>    lock(&dev->mode_config.mutex);
> 
>   *** DEADLOCK ***
> 
>   May be due to missing lock nesting notation
> 
>  7 locks held by kworker/0:3/88:
>   #0:  ("kacpi_notify"){++++.+}, at: [<ffffffff81068dfc>] process_one_work+0x14a/0x50b
>   #1:  ((&dpc->work)#2){+.+.+.}, at: [<ffffffff81068dfc>] process_one_work+0x14a/0x50b
>   #2:  ((acpi_lid_notifier).rwsem){++++.+}, at: [<ffffffff8106f874>] __blocking_notifier_call_chain+0x34/0x65
>   #3:  (&dev_priv->modeset_restore_lock){+.+.+.}, at: [<ffffffffa0664cf6>] intel_lid_notify+0x3c/0xd9 [i915]
>   #4:  (&dev->mode_config.mutex){+.+.+.}, at: [<ffffffffa02d0d4f>] drm_modeset_lock_all+0x3e/0xa6 [drm]
>   #5:  (crtc_ww_class_acquire){+.+.+.}, at: [<ffffffffa02d0d59>] drm_modeset_lock_all+0x48/0xa6 [drm]
>   #6:  (crtc_ww_class_mutex){+.+.+.}, at: [<ffffffffa02d0b2a>] modeset_lock+0x13c/0x1cd [drm]
> 
>  stack backtrace:
>  CPU: 0 PID: 88 Comm: kworker/0:3 Not tainted 4.6.0-rc1 #385
>  Hardware name: LENOVO 2776LEG/2776LEG, BIOS 6EET55WW (3.15 ) 12/19/2011
>  Workqueue: kacpi_notify acpi_os_execute_deferred
>   0000000000000000 ffff88022fd5f990 ffffffff8124af06 ffffffff825b39c0
>   ffffffff825b39c0 ffff88022fd5fa60 ffffffff8108f547 ffff88022fd5fa70
>   000000008108e817 ffff880230236cc0 0000000000000000 ffffffff825b39c0
>  Call Trace:
>   [<ffffffff8124af06>] dump_stack+0x67/0x90
>   [<ffffffff8108f547>] __lock_acquire+0xdb5/0xf71
>   [<ffffffff8108bd2c>] ? look_up_lock_class+0xbe/0x10a
>   [<ffffffff8108fae2>] lock_acquire+0x137/0x1cb
>   [<ffffffff8108fae2>] ? lock_acquire+0x137/0x1cb
>   [<ffffffffa063e6a4>] ? intel_display_resume+0x4a/0x12f [i915]
>   [<ffffffff8148202f>] mutex_lock_nested+0x7e/0x3a4
>   [<ffffffffa063e6a4>] ? intel_display_resume+0x4a/0x12f [i915]
>   [<ffffffffa063e6a4>] ? intel_display_resume+0x4a/0x12f [i915]
>   [<ffffffffa02d0b2a>] ? modeset_lock+0x13c/0x1cd [drm]
>   [<ffffffffa063e6a4>] intel_display_resume+0x4a/0x12f [i915]
>   [<ffffffffa063e6a4>] ? intel_display_resume+0x4a/0x12f [i915]
>   [<ffffffffa02d0b2a>] ? modeset_lock+0x13c/0x1cd [drm]
>   [<ffffffffa02d0b2a>] ? modeset_lock+0x13c/0x1cd [drm]
>   [<ffffffffa02d0bf7>] ? drm_modeset_lock+0x17/0x24 [drm]
>   [<ffffffffa02d0c8b>] ? drm_modeset_lock_all_ctx+0x87/0xa1 [drm]
>   [<ffffffffa0664d6a>] intel_lid_notify+0xb0/0xd9 [i915]
>   [<ffffffff8106f4c6>] notifier_call_chain+0x4a/0x6c
>   [<ffffffff8106f88d>] __blocking_notifier_call_chain+0x4d/0x65
>   [<ffffffff8106f8b9>] blocking_notifier_call_chain+0x14/0x16
>   [<ffffffffa0011215>] acpi_lid_send_state+0x83/0xad [button]
>   [<ffffffffa00112a6>] acpi_button_notify+0x41/0x132 [button]
>   [<ffffffff812b07df>] acpi_device_notify+0x19/0x1b
>   [<ffffffff812c8570>] acpi_ev_notify_dispatch+0x49/0x64
>   [<ffffffff812ab9fb>] acpi_os_execute_deferred+0x14/0x20
>   [<ffffffff81068f17>] process_one_work+0x265/0x50b
>   [<ffffffff810696f5>] worker_thread+0x1fc/0x2dd
>   [<ffffffff810694f9>] ? rescuer_thread+0x309/0x309
>   [<ffffffff810694f9>] ? rescuer_thread+0x309/0x309
>   [<ffffffff8106e2d6>] kthread+0xe0/0xe8
>   [<ffffffff8107bc47>] ? local_clock+0x19/0x22
>   [<ffffffff81484f42>] ret_from_fork+0x22/0x40
>   [<ffffffff8106e1f6>] ? kthread_create_on_node+0x1b5/0x1b5
> 
> Fixes: e2c8b8701e2d ("drm/i915: Use atomic helpers for suspend, v2.")
> Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
> Signed-off-by: Bjørn Mork <bjorn@...k.no>

Oops, that one's pretty silly. Unfortunately we don't have any such
machines in CI yet, and it wouldn't be possible to exercise the lid
notifier automatically.

Thanks for your fix, applied.
-Daniel

> ---
>  drivers/gpu/drm/i915/intel_lvds.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_lvds.c b/drivers/gpu/drm/i915/intel_lvds.c
> index 30a8403a8f4f..cd9fe609aefb 100644
> --- a/drivers/gpu/drm/i915/intel_lvds.c
> +++ b/drivers/gpu/drm/i915/intel_lvds.c
> @@ -478,11 +478,8 @@ static int intel_lid_notify(struct notifier_block *nb, unsigned long val,
>  	 * and as part of the cleanup in the hw state restore we also redisable
>  	 * the vga plane.
>  	 */
> -	if (!HAS_PCH_SPLIT(dev)) {
> -		drm_modeset_lock_all(dev);
> +	if (!HAS_PCH_SPLIT(dev))
>  		intel_display_resume(dev);
> -		drm_modeset_unlock_all(dev);
> -	}
>  
>  	dev_priv->modeset_restore = MODESET_DONE;
>  
> -- 
> 2.1.4
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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