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Date:   Fri, 24 Mar 2023 10:48:30 +0200
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc:     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,
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        ezequiel@vanguardiasur.com.ar, p.zabel@pengutronix.de,
        daniel.almeida@collabora.com, lkp@intel.com,
        oe-kbuild-all@lists.linux.dev, linux-media@vger.kernel.org,
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Subject: Re: [PATCH v2 2/8] media: videobuf2: Make bufs array dynamic
 allocated
Message-ID: <20230324084830.GA18895@pendragon.ideasonboard.com>
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 <b0018f7b-0556-0ac1-d2fa-89787a27fba1@xs4all.nl>
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On Fri, Mar 24, 2023 at 09:31:35AM +0100, Hans Verkuil wrote:
> 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.

The copy also needs to be protected by the lock.

> >> 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  }

-- 
Regards,

Laurent Pinchart