Re: [PATCH] drm/i915: Use rcu to defer freeing of irq_work

From: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915: Use rcu to defer freeing of irq_work
Date: Wed, 13 Dec 2017 14:34:10 +0200	[thread overview]
Message-ID: <1513168450.5228.40.camel@linux.intel.com> (raw)
In-Reply-To: <20171213094802.28243-1-chris@chris-wilson.co.uk>

On Wed, 2017-12-13 at 09:48 +0000, Chris Wilson wrote:
> It is illegal to perform an immediate free of the struct irq_work from
> inside the irq_work callback (as irq_work_run_list modifies work->flags
> after execution of the work->func()). As we use the irq_work to
> coordinate the freeing of the callback from two different softirq paths,
> we need to defer the kfree from inside our irq_work callback, for which
> we can use kfree_rcu.
> 
> Fixes: 81c0ed21aa91 ("drm/i915/fence: Avoid del_timer_sync() from inside a timer")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

<SNIP>

> @@ -367,6 +367,7 @@ struct i915_sw_dma_fence_cb {
>  	struct dma_fence *dma;
>  	struct timer_list timer;
>  	struct irq_work work;
> +	struct rcu_head rcu;

To reduce the chances of hitting the 4095 limit, maybe throw this right
after the base? OTOH, it'll yell if it breaks...

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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