linux-kernel - Re: [PATCH 5.4 40/49] drm/i915/gem: Serialise debugfs i915_gem

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Date:   Sat, 31 Oct 2020 12:42:48 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org, Chris Wilson <chris@...is-wilson.co.uk>,
        CQ Tang <cq.tang@...el.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>
Subject: Re: [PATCH 5.4 40/49] drm/i915/gem: Serialise debugfs
 i915_gem_objects with ctx->mutex

On Sat, Oct 31, 2020 at 12:35:36PM +0100, Greg Kroah-Hartman wrote:
> From: Chris Wilson <chris@...is-wilson.co.uk>
> 
> commit 4fe9af8e881d946bf60790eeb37a7c4f96e28382 upstream.
> 
> Since the debugfs may peek into the GEM contexts as the corresponding
> client/fd is being closed, we may try and follow a dangling pointer.
> However, the context closure itself is serialised with the ctx->mutex,
> so if we hold that mutex as we inspect the state coupled in the context,
> we know the pointers within the context are stable and will remain valid
> as we inspect their tables.
> 
> Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
> Cc: CQ Tang <cq.tang@...el.com>
> Cc: Daniel Vetter <daniel.vetter@...el.com>
> Cc: stable@...r.kernel.org
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@...el.com>
> Link: https://patchwork.freedesktop.org/patch/msgid/20200723172119.17649-3-chris@chris-wilson.co.uk
> (cherry picked from commit 102f5aa491f262c818e607fc4fee08a724a76c69)
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@...el.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> 
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c |    2 ++
>  1 file changed, 2 insertions(+)

Oops, nope, this breaks the build here, now dropping it...

greg k-h