Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <be12c081-61a9-f476-7afe-b1bb78c35dea@collabora.com>
Date:   Fri, 24 Mar 2023 01:19:15 +0300
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.8.0
Subject: Re: [PATCH v3 2/2] drm/virtio: Support sync objects
Content-Language: en-US
From:   Dmitry Osipenko <dmitry.osipenko@collabora.com>
To:     Rob Clark <robdclark@gmail.com>
Cc:     David Airlie <airlied@redhat.com>,
        Gerd Hoffmann <kraxel@redhat.com>,
        Gurchetan Singh <gurchetansingh@chromium.org>,
        Chia-I Wu <olvaffe@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
        =?UTF-8?B?TWFyZWsgT2zFocOhaw==?= <maraeo@gmail.com>,
        Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>,
        Emil Velikov <emil.velikov@collabora.com>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        kernel@collabora.com, virtualization@lists.linux-foundation.org
References: <20230323190340.950875-1-dmitry.osipenko@collabora.com>
 <20230323190340.950875-3-dmitry.osipenko@collabora.com>
 <CAF6AEGs28wzuXc3w+qYvcUH+dT271w=dtxmzKfR6zgHqXqjMzQ@mail.gmail.com>
 <889ce0e7-f61a-ed0a-35d5-1a9290521d49@collabora.com>
In-Reply-To: <889ce0e7-f61a-ed0a-35d5-1a9290521d49@collabora.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 3/24/23 00:51, Dmitry Osipenko wrote:
> On 3/24/23 00:18, Rob Clark wrote:
> ...
>>> +static int
>>> +virtio_gpu_parse_deps(struct virtio_gpu_submit *submit)
>>> +{
>>> +       struct drm_virtgpu_execbuffer *exbuf = submit->exbuf;
>>> +       struct drm_virtgpu_execbuffer_syncobj syncobj_desc;
>>> +       size_t syncobj_stride = exbuf->syncobj_stride;
>>> +       struct drm_syncobj **syncobjs;
>>> +       int ret = 0, i;
>>> +
>>> +       if (!submit->num_in_syncobjs)
>>> +               return 0;
>>> +
>>> +       syncobjs = kcalloc(submit->num_in_syncobjs, sizeof(*syncobjs),
>>> +                          GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY);
>> I *think*, assuming I'm reading where this is called correctly (kinda
>> wish git would show more lines of context by default) that these don't
>> need to be NOWARN|NORETRY (same for post_deps).  I guess you inherited
>> this from drm/msm, where I appear to have forgotten to update the
>> syncobj path in commit f0de40a131d9 ("drm/msm: Reorder lock vs submit
>> alloc").  I don't see anything obvious that would require NORETRY, but
>> lockdep should be able to tell you otherwise if needed.
> 
> The NORETRY should prevent waking up OOM killer, it shouldn't help with
> lockdep. Nothing prevents userspace from giving a big number of
> num_in_syncobjs. But perhaps indeed not very practical to care about
> this case, given that other similar memalloc paces of execbuffer_ioctl()
> aren't using NORETRY. Alright, let's drop it in v4.
> 

Although no, there is only a kvmalloc_array() in the code and vmalloc
uses NOWARN and NORETRY flags implicitly. May be better switch to use
kvmalloc everywhere, for consistency. Technically, vmalloc shouldn't
ever be needed for a submit code path and kmalloc should be enough. On
the other hand, vmalloc acts like kmalloc until there is no enough
contig memory.

-- 
Best regards,
Dmitry