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Date:   Tue, 19 Jan 2021 10:35:38 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Christian =?iso-8859-1?Q?K=F6nig?= 
        <ckoenig.leichtzumerken@gmail.com>
Cc:     daniel@ffwll.ch, mingo@redhat.com, will@kernel.org,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/syncobj: make lockdep complain on WAIT_FOR_SUBMIT v2
Message-ID: <YAan6haGjnIlNIoJ@hirez.programming.kicks-ass.net>
References: <20210118180334.43714-1-christian.koenig@amd.com>
 <20210118180334.43714-2-christian.koenig@amd.com>
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In-Reply-To: <20210118180334.43714-2-christian.koenig@amd.com>
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On Mon, Jan 18, 2021 at 07:03:34PM +0100, Christian K?nig wrote:

> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index 6e74e6745eca..f51458615158 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -387,6 +387,13 @@ int drm_syncobj_find_fence(struct drm_file *file_private,
>  	if (!syncobj)
>  		return -ENOENT;
>  
> +	/* Waiting for userspace with locks help is illegal cause that can
> +	 * trivial deadlock with page faults for example. Make lockdep complain
> +	 * about it early on.
> +	 */

Egads, the cursed comment style is spreading :/

> +	if (flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT)
> +		lockdep_assert_none_held_once();
> +

Should this not be part of drm_syncobj_fence_add_wait() instead? Also,
do you want to sprinkle might_sleep() around ?

>  	*fence = drm_syncobj_fence_get(syncobj);
>  	drm_syncobj_put(syncobj);
>  
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h