linux-kernel - Re: [PATCH v2] drm/ttm: Silence randstruct warning about casting struct file

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Message-ID: <20250502043149.GW2023217@ZenIV>
Date: Fri, 2 May 2025 05:31:49 +0100
From: Al Viro <viro@...iv.linux.org.uk>
To: Matthew Brost <matthew.brost@...el.com>
Cc: Kees Cook <kees@...nel.org>,
	Thomas Hellström <thomas.hellstrom@...ux.intel.com>,
	Christian Koenig <christian.koenig@....com>,
	Somalapuram Amaranath <Amaranath.Somalapuram@....com>,
	Huang Rui <ray.huang@....com>,
	Matthew Auld <matthew.auld@...el.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH v2] drm/ttm: Silence randstruct warning about casting
 struct file

On Thu, May 01, 2025 at 09:26:25PM -0700, Matthew Brost wrote:

> I;m fairly certain is just aliasing... but I do understand a file cannot
> be embedded. Would comment help here indicating no other fields should
> be added to ttm_backup without struct file be converted to pointer or
> that just to risky?

What exactly are you trying to do there?  IOW, is that always supposed to
be a struct file, or something dependent upon something in struct ttm_tt
instance, or...?

And what is the lifecycle of that thing?  E.g. what is guaranteed about
ttm_backup_fini() vs. functions accessing the damn thing?  Are they
serialized on something/tied to lifecycle stages of struct ttm_tt?