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

[Sharma, Shashank]

On 23/03/2024 15:52, Johannes Weiner wrote:
> 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?

Ah, sorry I missed this due to some parallel work, and just realized the 
memcpy/volatile limitation.

I also feel the need of protecting MQD read under a lock to avoid 
parallel change in MQD while we do byte-by-byte copy, but I will add 
that in my to-do list.

Please feel free to use my R-b.

- Shashank

> Thanks