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Running the contrib/test/test-media script in v4l-utils with the vicodec argument will cause this kernel warning: [ 372.298824] ------------[ cut here ]------------ [ 372.298848] DEBUG_LOCKS_WARN_ON(lock->magic != lock) [ 372.298896] WARNING: CPU: 11 PID: 2220 at kernel/locking/mutex.c:938 __mutex_lock+0x919/0xc10 [ 372.298907] Modules linked in: vicodec v4l2_mem2mem vivid rc_cec v4l2_tpg videobuf2_dma_contig cec rc_core v4l2_dv_timings videobuf2_vmalloc videobuf2_memops videobuf2_v4l2 videobuf2_common videodev mc vmw_balloon vmw_vmci button vmwgfx [last unloaded: vimc] [ 372.298961] CPU: 11 PID: 2220 Comm: sleep Not tainted 5.4.0-rc1-test-no #150 [ 372.298970] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/29/2019 [ 372.298983] RIP: 0010:__mutex_lock+0x919/0xc10 [ 372.298995] Code: 59 83 e8 9a fc 16 ff 44 8b 05 23 61 38 01 45 85 c0 0f 85 ef f7 ff ff 48 c7 c6 a0 1f 87 82 48 c7 c7 a0 1e 87 82 e8 cd bb f7 fe <0f> 0b e9 d5 f7 ff ff f6 c3 04 0f 84 3b fd ff ff 49 89 df 41 83 e7 [ 372.299004] RSP: 0018:ffff8881b400fb80 EFLAGS: 00010286 [ 372.299014] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 [ 372.299022] RDX: 0000000000000003 RSI: 0000000000000004 RDI: ffffed1036801f62 [ 372.299030] RBP: ffff8881b400fcf0 R08: ffffffff81217c91 R09: fffffbfff061c271 [ 372.299038] R10: fffffbfff061c270 R11: ffffffff830e1383 R12: ffff88814761dc80 [ 372.299046] R13: 0000000000000000 R14: ffff88814761cbf0 R15: ffff88814761d030 [ 372.299055] FS: 0000000000000000(0000) GS:ffff8881b68c0000(0000) knlGS:0000000000000000 [ 372.299063] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 372.299071] CR2: 00007f606d78aa20 CR3: 0000000003013002 CR4: 00000000001606e0 [ 372.299153] Call Trace: [ 372.299176] ? __kasan_slab_free+0x12f/0x180 [ 372.299187] ? kmem_cache_free+0x9b/0x250 [ 372.299200] ? do_exit+0xcdf/0x1200 [ 372.299210] ? do_group_exit+0x85/0x130 [ 372.299220] ? __x64_sys_exit_group+0x23/0x30 [ 372.299231] ? do_syscall_64+0x5e/0x1c0 [ 372.299241] ? entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 372.299295] ? v4l2_release+0xed/0x190 [videodev] [ 372.299309] ? mutex_lock_io_nested+0xb80/0xb80 [ 372.299323] ? find_held_lock+0x85/0xa0 [ 372.299335] ? fsnotify+0x5b0/0x600 [ 372.299351] ? locks_remove_file+0x78/0x2b0 [ 372.299363] ? __fsnotify_update_child_dentry_flags.part.0+0x170/0x170 [ 372.299383] ? vidioc_querycap+0x50/0x50 [vicodec] [ 372.299426] ? v4l2_release+0xed/0x190 [videodev] [ 372.299467] v4l2_release+0xed/0x190 [videodev] [ 372.299484] __fput+0x15a/0x390 [ 372.299499] task_work_run+0xb2/0xe0 [ 372.299512] do_exit+0x4d0/0x1200 [ 372.299528] ? do_user_addr_fault+0x367/0x610 [ 372.299538] ? release_task+0x990/0x990 [ 372.299552] ? rwsem_spin_on_owner+0x170/0x170 [ 372.299567] ? vmacache_find+0xb2/0x100 [ 372.299580] do_group_exit+0x85/0x130 [ 372.299592] __x64_sys_exit_group+0x23/0x30 [ 372.299602] do_syscall_64+0x5e/0x1c0 [ 372.299614] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 372.299624] RIP: 0033:0x7f606d74a9d6 [ 372.299640] Code: Bad RIP value. [ 372.299648] RSP: 002b:00007fff65364468 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7 [ 372.299658] RAX: ffffffffffffffda RBX: 00007f606d83b760 RCX: 00007f606d74a9d6 [ 372.299666] RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000 [ 372.299673] RBP: 0000000000000000 R08: 00000000000000e7 R09: ffffffffffffff80 [ 372.299681] R10: 00007fff65364334 R11: 0000000000000246 R12: 00007f606d83b760 [ 372.299689] R13: 0000000000000002 R14: 00007f606d844428 R15: 0000000000000000 [ 372.299704] ---[ end trace add7d62ca4bc65e3 ]--- This is caused by media_device_cleanup() which destroys v4l2_dev->mdev->req_queue_mutex. But v4l2_release() tries to lock that mutex after media_device_cleanup() is called. By moving media_device_cleanup() to the v4l2_device's release function it is guaranteed that the mutex is valid whenever v4l2_release is called. Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.