[Intel-gfx] [PATCH] drm/syncobj: Avoid kmalloc(GFP_KERNEL) under spinlock

[Chris Wilson]

Quoting Chunming Zhou (2018-10-25 16:08:31)
> drivers/gpu/drm/drm_syncobj.c:202:4-14: ERROR: function drm_syncobj_find_signal_pt_for_point called on line 390 inside lock on line 389 but uses GFP_KERNEL
> 
>   Find functions that refer to GFP_KERNEL but are called with locks held.
> 
> Generated by: scripts/coccinelle/locks/call_kern.cocci
> 
> v2:
> syncobj->timeline still needs protect.
> 
> v3:
> use a global signaled fence instead of re-allocation.
> 
> v4:
> Don't need moving lock.
> Don't expose func.
> 
> Tested by: syncobj_wait and ./deqp-vk -n dEQP-VK.*semaphore* with
> lock debug kernel options enabled.
> 
> Signed-off-by: Chunming Zhou <david1.zhou at amd.com>
> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Cc: intel-gfx at lists.freedesktop.org
> Cc: Christian König <easy2remember.chk at googlemail.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> CC: Julia Lawall <julia.lawall at lip6.fr>
> ---
> -       return NULL;
> +out:
> +       return f;

As it reduced to just a return, I'd probably have gone with multiple
returns in this instance. Still the compiler should have done the
equivalent and jumped to a single ret.

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris