On Fri, Mar 24, 2023 at 09:56:34AM +0100, Benjamin Gaignard wrote: > > Le 24/03/2023 à 09:52, Hans Verkuil a écrit : > > On 24/03/2023 09:48, Laurent Pinchart wrote: > > > 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@xxxxxxxxx/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@xxxxxxxxx> > > > > > > | Reported-by: Dan Carpenter <error27@xxxxxxxxx> > > > > > > | Link: https://lore.kernel.org/r/202303240148.lKRnUqW9-lkp@xxxxxxxxx/ > > > > > > > > > > > > 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. > > I suspect that that is not needed, since you shouldn't be able to add buffers here > > since a mutex should be held at this time. > > > > That said, it's something that Benjamin needs to analyze. I spent some time looking through the call sites of vb2_get_buffer() and how those can be called and it turned out to be a massive list of code paths, including a lot of calls originating from codec drivers calling vb2_find_buffer() in random contexts (possibly even interrupt). So a spinlock protecting the array pointer makes sense indeed. > > Does using GFP_ATOMIC is problematic ? > Yes, because the ability to reclaim memory is drastically limited and the allocation is more likely to fail (as in: it's actually possible). (And generally the time with interrupts disabled should be minimized to keep system latency reasonable.) Best regards, Tomasz
