linux-kernel - Re: [PATCH 3/3] drm/i915: use might_lock_nested in get

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Date:   Fri, 23 Aug 2019 10:49:56 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH 3/3] drm/i915: use might_lock_nested in get_pages
 annotation

On Tue, Aug 20, 2019 at 10:19:51AM +0200, Daniel Vetter wrote:
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> index a0b1fa8a3224..b3fd6aac93bc 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> @@ -233,10 +233,26 @@ void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj,
>  int ____i915_gem_object_get_pages(struct drm_i915_gem_object *obj);
>  int __i915_gem_object_get_pages(struct drm_i915_gem_object *obj);
>  
> +enum i915_mm_subclass { /* lockdep subclass for obj->mm.lock/struct_mutex */
> +	I915_MM_NORMAL = 0,
> +	/*
> +	 * Only used by struct_mutex, when called "recursively" from
> +	 * direct-reclaim-esque. Safe because there is only every one
> +	 * struct_mutex in the entire system. */
> +	I915_MM_SHRINKER = 1,
> +	/*
> +	 * Used for obj->mm.lock when allocating pages. Safe because the object
> +	 * isn't yet on any LRU, and therefore the shrinker can't deadlock on
> +	 * it. As soon as the object has pages, obj->mm.lock nests within
> +	 * fs_reclaim.
> +	 */
> +	I915_MM_GET_PAGES = 1,

Those comments are inconsistently styled; if you move them, might as
well fix that too :-)

> +};
> +