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Running the contrib/test/test-media script in v4l-utils with the vim2m argument will cause this kernel warning: [ 554.430157] ------------[ cut here ]------------ [ 554.433034] DEBUG_LOCKS_WARN_ON(lock->magic != lock) [ 554.433064] WARNING: CPU: 0 PID: 616 at kernel/locking/mutex.c:938 __mutex_lock+0xd7a/0x1380 [ 554.439736] Modules linked in: vim2m v4l2_mem2mem vivid rc_cec videobuf2_dma_contig v4l2_dv_timings cec videobuf2_vmalloc videobuf2_memops v4l2_tpg videobuf2_v4l2 videobuf2_common videodev mc rc_core [last unloaded: vivid] [ 554.445794] CPU: 0 PID: 616 Comm: sleep Not tainted 5.4.0-rc1-virtme #1 [ 554.448481] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-0-ga698c8995f-prebuilt.qemu.org 04/01/2014 [ 554.453088] RIP: 0010:__mutex_lock+0xd7a/0x1380 [ 554.454955] Code: d2 0f 85 de 05 00 00 44 8b 05 82 d9 f7 00 45 85 c0 0f 85 bf f3 ff ff 48 c7 c6 e0 30 a6 b7 48 c7 c7 e0 2e a6 b7 e8 5c 76 36 fe <0f> 0b e9 a5 f3 ff ff 65 48 8b 1c 25 80 ef 01 00 be 08 00 00 00 48 [ 554.462836] RSP: 0018:ffff88803a4cfad0 EFLAGS: 00010282 [ 554.465129] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffffb5a3d24f [ 554.468143] RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffffffffb85273f4 [ 554.471000] RBP: ffff88803a4cfc50 R08: fffffbfff701e681 R09: fffffbfff701e681 [ 554.473990] R10: fffffbfff701e680 R11: ffffffffb80f3403 R12: 0000000000000000 [ 554.476831] R13: dffffc0000000000 R14: ffffffffb9714f00 R15: ffff888053103fc8 [ 554.479622] FS: 00007fac6358a540(0000) GS:ffff88805d000000(0000) knlGS:0000000000000000 [ 554.482673] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 554.484949] CR2: 00007fac6343faf0 CR3: 0000000036c22000 CR4: 00000000003406f0 [ 554.487811] Call Trace: [ 554.488860] ? v4l2_release+0x1b8/0x390 [videodev] [ 554.490818] ? do_exit+0x946/0x2980 [ 554.492269] ? mutex_lock_io_nested+0x1250/0x1250 [ 554.494128] ? __lock_acquire+0xe90/0x3c30 [ 554.495774] ? fsnotify_first_mark+0x120/0x120 [ 554.497487] ? vim2m_device_release+0x50/0x50 [vim2m] [ 554.499469] ? v4l2_release+0x1b8/0x390 [videodev] [ 554.501493] v4l2_release+0x1b8/0x390 [videodev] [ 554.503430] __fput+0x256/0x790 [ 554.504711] task_work_run+0x109/0x190 [ 554.506145] do_exit+0x95e/0x2980 [ 554.507421] ? vfs_lock_file+0x21/0xf0 [ 554.509013] ? find_held_lock+0x33/0x1c0 [ 554.510382] ? __close_fd+0xee/0x190 [ 554.511862] ? release_task.part.21+0x1310/0x1310 [ 554.513701] ? lock_downgrade+0x6d0/0x6d0 [ 554.515299] do_group_exit+0xeb/0x2d0 [ 554.516862] __x64_sys_exit_group+0x35/0x40 [ 554.518610] do_syscall_64+0x90/0x450 [ 554.520142] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 554.522289] RIP: 0033:0x7fac6348ecf6 [ 554.523876] Code: Bad RIP value. [ 554.525294] RSP: 002b:00007ffe6373dc58 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7 [ 554.528555] RAX: ffffffffffffffda RBX: 00007fac6357f760 RCX: 00007fac6348ecf6 [ 554.531537] RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000 [ 554.534709] RBP: 0000000000000000 R08: 00000000000000e7 R09: ffffffffffffff80 [ 554.536752] R10: 00007ffe6373db24 R11: 0000000000000246 R12: 00007fac6357f760 [ 554.538643] R13: 0000000000000002 R14: 00007fac63588428 R15: 0000000000000000 [ 554.540634] irq event stamp: 21731 [ 554.541618] hardirqs last enabled at (21731): [<ffffffffb75b3cd4>] _raw_spin_unlock_irq+0x24/0x30 [ 554.544145] hardirqs last disabled at (21730): [<ffffffffb75b3ada>] _raw_spin_lock_irq+0xa/0x40 [ 554.547027] softirqs last enabled at (20148): [<ffffffffb780064d>] __do_softirq+0x64d/0x906 [ 554.550385] softirqs last disabled at (19857): [<ffffffffb5926bd5>] irq_exit+0x175/0x1a0 [ 554.553668] ---[ end trace a389c80c2ca84244 ]--- 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 video_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.