linux-kernel - Re: [PATCH] drm/amdgpu: fix deadlock while reading mqd from debugfs

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Message-ID: <20240323145247.GC448621@cmpxchg.org>
Date: Sat, 23 Mar 2024 10:52:47 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Christian König <ckoenig.leichtzumerken@...il.com>
Cc: Alex Deucher <alexander.deucher@....com>,
	"Sharma, Shashank" <Shashank.Sharma@....com>,
	Christian König <christian.koenig@....com>,
	amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/amdgpu: fix deadlock while reading mqd from debugfs

On Thu, Mar 14, 2024 at 01:09:57PM -0400, Johannes Weiner wrote:
> Hello,
> 
> On Fri, Mar 08, 2024 at 12:32:33PM +0100, Christian König wrote:
> > Am 07.03.24 um 23:07 schrieb Johannes Weiner:
> > > Lastly I went with an open loop instead of a memcpy() as I wasn't
> > > sure if that memory is safe to address a byte at at time.
> 
> Shashank pointed out to me in private that byte access would indeed be
> safe. However, after actually trying it it won't work because memcpy()
> doesn't play nice with mqd being volatile:
> 
> /home/hannes/src/linux/linux/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c: In function 'amdgpu_debugfs_mqd_read':
> /home/hannes/src/linux/linux/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c:550:22: warning: passing argument 1 of '__builtin_dynamic_object_size' discards 'volatil' qualifier from pointer target type [-Wdiscarded-qualifiers]
>   550 |         memcpy(kbuf, mqd, ring->mqd_size);
> 
> So I would propose leaving the patch as-is. Shashank, does that sound
> good to you?

Friendly ping :)

Shashank, is your Reviewed-by still good for this patch, given the
above?

Thanks