Re: [PATCH] drm/i915: Fix deadlock during driver init on ILK

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Apr 25, 2014 at 10:11:51PM +0300, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> We have a struct_mutex deadlock during driver init on ILK
> 
> [   54.320273] =============================================
> [   54.320371] [ INFO: possible recursive locking detected ]
> [   54.320471] 3.15.0-rc2-flip_race+ #2 Not tainted
> [   54.320567] ---------------------------------------------
> [   54.320665] modprobe/2178 is trying to acquire lock:
> [   54.320762]  (&dev->struct_mutex){+.+.+.}, at: [<ffffffffa0568b05>] intel_enable_gt_powersave+0xa5/0x9d0 [i915]
> [   54.321111]
> [   54.321111] but task is already holding lock:
> [   54.321250]  (&dev->struct_mutex){+.+.+.}, at: [<ffffffffa05b4c2e>] intel_modeset_init_hw+0x3e/0x60 [i915]
> [   54.321583]
> [   54.321583] other info that might help us debug this:
> [   54.321724]  Possible unsafe locking scenario:
> [   54.321724]
> [   54.321863]        CPU0
> [   54.321954]        ----
> [   54.322046]   lock(&dev->struct_mutex);
> [   54.322221]   lock(&dev->struct_mutex);
> [   54.322397]
> [   54.322397]  *** DEADLOCK ***
> [   54.322397]
> [   54.322638]  May be due to missing lock nesting notation
> [   54.322638]
> [   54.322781] 4 locks held by modprobe/2178:
> [   54.322875]  #0:  (&dev->mutex){......}, at: [<ffffffff813592eb>] __driver_attach+0x5b/0xb0
> [   54.323230]  #1:  (&dev->mutex){......}, at: [<ffffffff813592f9>] __driver_attach+0x69/0xb0
> [   54.323582]  #2:  (drm_global_mutex){+.+.+.}, at: [<ffffffffa04e1e0d>] drm_dev_register+0x2d/0x120 [drm]
> [   54.323945]  #3:  (&dev->struct_mutex){+.+.+.}, at: [<ffffffffa05b4c2e>] intel_modeset_init_hw+0x3e/0x60 [i915]
> 
> This regression got introduced in:
>  commit 586d5270b60dc1f35cc3ca982d403765bad77965
>  Author: Imre Deak <imre.deak@intel.com>
>  Date:   Mon Apr 14 20:24:28 2014 +0300
> 
>     drm/i915: move getting struct_mutex lower in the callstack during GPU reset
> 
> Fix the problem by not taking struct_mutex around intel_enable_gt_powersave()
> in intel_modeset_init_hw() since intel_enable_gt_powersave() now grabs the
> mutex itself.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

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