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Date:   Fri, 24 Mar 2023 09:31:35 +0100
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Subject: Re: [PATCH v2 2/8] media: videobuf2: Make bufs array dynamic
 allocated
To:     Benjamin Gaignard <benjamin.gaignard@collabora.com>,
        Dan Carpenter <error27@gmail.com>, oe-kbuild@lists.linux.dev,
        tfiga@chromium.org, m.szyprowski@samsung.com, mchehab@kernel.org,
        ming.qian@nxp.com, shijie.qin@nxp.com, eagle.zhou@nxp.com,
        bin.liu@mediatek.com, matthias.bgg@gmail.com,
        angelogioacchino.delregno@collabora.com, tiffany.lin@mediatek.com,
        andrew-ct.chen@mediatek.com, yunfei.dong@mediatek.com,
        stanimir.k.varbanov@gmail.com, quic_vgarodia@quicinc.com,
        agross@kernel.org, andersson@kernel.org, konrad.dybcio@linaro.org,
        ezequiel@vanguardiasur.com.ar, p.zabel@pengutronix.de,
        daniel.almeida@collabora.com, laurent.pinchart@ideasonboard.com
Cc:     lkp@intel.com, oe-kbuild-all@lists.linux.dev,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
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References: <4e2cb832-de83-4ba6-bd8a-119a19038cfe@kili.mountain>
 <a88b93cc-a81f-6186-09fc-02223867e677@collabora.com>
Content-Language: en-US
From:   Hans Verkuil <hverkuil-cisco@xs4all.nl>
In-Reply-To: <a88b93cc-a81f-6186-09fc-02223867e677@collabora.com>
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On 24/03/2023 09:11, Benjamin Gaignard wrote:
> 
> Le 24/03/2023 à 06:01, Dan Carpenter a écrit :
>> Hi Benjamin,
>>
>> https://git-scm.com/docs/git-format-patch#_base_tree_information]
>>
>> url:    https://github.com/intel-lab-lkp/linux/commits/Benjamin-Gaignard/media-videobuf2-Access-vb2_queue-bufs-array-through-helper-functions/20230321-183154
>> base:   git://linuxtv.org/media_tree.git master
>> patch link:    https://lore.kernel.org/r/20230321102855.346732-3-benjamin.gaignard%40collabora.com
>> patch subject: [PATCH v2 2/8] media: videobuf2: Make bufs array dynamic allocated
>> config: arm64-randconfig-m041-20230319 (https://download.01.org/0day-ci/archive/20230324/202303240148.lKRnUqW9-lkp@intel.com/config)
>> compiler: aarch64-linux-gcc (GCC) 12.1.0
>>
>> If you fix the issue, kindly add following tag where applicable
>> | Reported-by: kernel test robot <lkp@intel.com>
>> | Reported-by: Dan Carpenter <error27@gmail.com>
>> | Link: https://lore.kernel.org/r/202303240148.lKRnUqW9-lkp@intel.com/
>>
>> smatch warnings:
>> include/media/videobuf2-core.h:1272 vb2_queue_add_buffer() warn: sleeping in atomic context
>> drivers/media/common/videobuf2/videobuf2-core.c:2456 vb2_core_queue_init() warn: Please consider using kcalloc instead of kmalloc_array
>>
>> vim +1272 include/media/videobuf2-core.h
>>
>> 625d46c1c1fe8e Benjamin Gaignard 2023-03-21  1263  static inline bool vb2_queue_add_buffer(struct vb2_queue *q, struct vb2_buffer *vb)
>> 625d46c1c1fe8e Benjamin Gaignard 2023-03-21  1264  {
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1265      bool ret = false;
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1266
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1267      spin_lock(&q->bufs_lock);
>>                                                          ^^^^^^^^^^^^^^^^^^^^^^^
>> Holding a spin lock.
>>
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1268
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1269      if (vb->index >= q->max_num_bufs) {
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1270          struct vb2_buffer **tmp;
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1271
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21 @1272          tmp = krealloc_array(q->bufs, q->max_num_bufs * 2, sizeof(*q->bufs), GFP_KERNEL);
>>                                                                                                                                       ^^^^^^^^^^
>> Sleeping allocation.  GFP_ATOMIC?  Or is there a way to move the
>> allocation outside the lock?
> 
> I will add GFP_ATOMIC flag in next version.

No need. Instead, don't use realloc here, just allocate a new array, copy over all
the data from the old, and then switch q->bufs with the spinlock held. Then you
can free the old one.

It's only when you update q->bufs that you need the lock.

Regards,

	Hans

> 
> Thanks for your help,
> Benjamin
> 
>>
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1273          if (!tmp)
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1274              goto realloc_failed;
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1275
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1276          q->max_num_bufs *= 2;
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1277          q->bufs = tmp;
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1278      }
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1279
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1280      if (vb->index < q->max_num_bufs) {
>> 625d46c1c1fe8e Benjamin Gaignard 2023-03-21  1281          q->bufs[vb->index] = vb;
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1282          ret = true;
>> 625d46c1c1fe8e Benjamin Gaignard 2023-03-21  1283      }
>> 625d46c1c1fe8e Benjamin Gaignard 2023-03-21  1284
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1285  realloc_failed:
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1286      spin_unlock(&q->bufs_lock);
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1287
>> 487d3f14d12ecf Benjamin Gaignard 2023-03-21  1288      return ret;
>> 625d46c1c1fe8e Benjamin Gaignard 2023-03-21  1289  }
>>