8ffd573c25
Running the contrib/test/test-media script in v4l-utils with the vivid argument will cause this kernel warning: [ 104.748720] videodev: v4l2_release [ 104.748731] ------------[ cut here ]------------ [ 104.748750] DEBUG_LOCKS_WARN_ON(lock->magic != lock) [ 104.748790] WARNING: CPU: 6 PID: 1823 at kernel/locking/mutex.c:938 __mutex_lock+0x919/0xc10 [ 104.748800] Modules linked in: rc_cec vivid 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 [ 104.748845] CPU: 6 PID: 1823 Comm: sleep Not tainted 5.4.0-rc1-test-no #150 [ 104.748853] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/29/2019 [ 104.748867] RIP: 0010:__mutex_lock+0x919/0xc10 [ 104.748878] 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 [ 104.748886] RSP: 0018:ffff88811a357b80 EFLAGS: 00010286 [ 104.748895] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 [ 104.748902] RDX: 0000000000000003 RSI: 0000000000000004 RDI: ffffed102346af62 [ 104.748910] RBP: ffff88811a357cf0 R08: ffffffff81217c91 R09: fffffbfff061c271 [ 104.748917] R10: fffffbfff061c270 R11: ffffffff830e1383 R12: ffff8881a46103c0 [ 104.748924] R13: 0000000000000000 R14: ffff8881a4614f90 R15: ffff8881a46153d0 [ 104.748933] FS: 0000000000000000(0000) GS:ffff8881b6780000(0000) knlGS:0000000000000000 [ 104.748940] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 104.748949] CR2: 00007f163fc9ca20 CR3: 0000000003013004 CR4: 00000000001606e0 [ 104.749036] Call Trace: [ 104.749051] ? _raw_spin_unlock+0x1f/0x30 [ 104.749067] ? llist_add_batch+0x33/0x50 [ 104.749081] ? tick_nohz_tick_stopped+0x19/0x30 [ 104.749130] ? v4l2_release.cold+0x6c/0xd6 [videodev] [ 104.749143] ? mutex_lock_io_nested+0xb80/0xb80 [ 104.749153] ? vprintk_emit+0xf2/0x220 [ 104.749191] ? vivid_req_validate+0x40/0x40 [vivid] [ 104.749201] ? printk+0xad/0xde [ 104.749211] ? kmsg_dump_rewind_nolock+0x54/0x54 [ 104.749226] ? locks_remove_file+0x78/0x2b0 [ 104.749248] ? __fsnotify_update_child_dentry_flags.part.0+0x170/0x170 [ 104.749281] ? vivid_req_validate+0x40/0x40 [vivid] [ 104.749321] ? v4l2_release.cold+0x6c/0xd6 [videodev] [ 104.749361] v4l2_release.cold+0x6c/0xd6 [videodev] [ 104.749378] __fput+0x15a/0x390 [ 104.749393] task_work_run+0xb2/0xe0 [ 104.749407] do_exit+0x4d0/0x1200 [ 104.749422] ? do_user_addr_fault+0x367/0x610 [ 104.749431] ? release_task+0x990/0x990 [ 104.749449] ? rwsem_spin_on_owner+0x170/0x170 [ 104.749463] ? vmacache_find+0xb2/0x100 [ 104.749476] do_group_exit+0x85/0x130 [ 104.749487] __x64_sys_exit_group+0x23/0x30 [ 104.749500] do_syscall_64+0x5e/0x1c0 [ 104.749511] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 104.749520] RIP: 0033:0x7f163fc5c9d6 [ 104.749536] Code: Bad RIP value. [ 104.749543] RSP: 002b:00007ffe6f3bec58 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7 [ 104.749553] RAX: ffffffffffffffda RBX: 00007f163fd4d760 RCX: 00007f163fc5c9d6 [ 104.749560] RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000 [ 104.749567] RBP: 0000000000000000 R08: 00000000000000e7 R09: ffffffffffffff80 [ 104.749574] R10: 00007ffe6f3beb24 R11: 0000000000000246 R12: 00007f163fd4d760 [ 104.749581] R13: 0000000000000002 R14: 00007f163fd56428 R15: 0000000000000000 [ 104.749597] ---[ end trace 66f20f73fc0daf79 ]--- 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@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.