Hello!
I started testing locks from my SDR drivers and ended up unexpected
warnings. Now I have looked quite a lot of things and read carefully
many times v4l2 framework documentation [1]. V4L2 locking model is not
very clear for me, but I understand there is 2 mutex, one for
serializing IOCTLs and one for serializing videobuf2 operations. And top
of that there is spinlock inside driver for frame-buffers. It hard to
say very much about those locks which are hidden inside v4l2 - only
pointer passed from driver. Maybe it is possible to get rid of that by
using own locks inside driver (passing NULL mutexes to v4l2/vb2 gives
possibility to use own locking)?
[1] Documentation/video4linux/v4l2-framework.txt
After the MSi3101 SDR driver test failures I decided to test some other
drivers to see what happens. As I don't have many webcams I decided to
test vivi and surprise, same error is reported.
I don't know enough v4l2 / vb2 internals to say much about these. But I
think I don't care to try fix SDR drivers as that same error seems to be
reported other devices too. Maybe it is some corner case or false
positive. Anyhow, it could be nice to get rid of it.
joulu 22 18:26:31 localhost.localdomain kernel: vivi-000: V4L2 device
registered as video0
joulu 22 18:26:31 localhost.localdomain kernel: Video Technology
Magazine Virtual Video Capture Board ver 0.8.1 successfully loaded.
joulu 22 18:26:31 localhost.localdomain colord[630]: Device added:
sysfs-/dev/video0
joulu 22 18:26:43 localhost.localdomain chronyd[563]: Selected source
62.237.86.234
joulu 22 18:26:51 localhost.localdomain kernel: joulu 22 18:26:51
localhost.localdomain kernel:
======================================================
joulu 22 18:26:51 localhost.localdomain kernel: [ INFO: possible
circular locking dependency detected ]
joulu 22 18:26:51 localhost.localdomain kernel: 3.13.0-rc1+ #77 Tainted:
G C O
joulu 22 18:26:51 localhost.localdomain kernel:
-------------------------------------------------------
joulu 22 18:26:51 localhost.localdomain kernel: video_source:sr/32072 is
trying to acquire lock:
joulu 22 18:26:51 localhost.localdomain kernel:
(&dev->mutex#2){+.+.+.}, at: [<ffffffffa073fde3>] vb2_fop_mmap+0x33/0x90
[videobuf2_core]
joulu 22 18:26:51 localhost.localdomain kernel:
but task is already
holding lock:
joulu 22 18:26:51 localhost.localdomain kernel:
(&mm->mmap_sem){++++++}, at: [<ffffffff8117825f>] vm_mmap_pgoff+0x6f/0xc0
joulu 22 18:26:51 localhost.localdomain kernel:
which lock already
depends on the new lock.
joulu 22 18:26:51 localhost.localdomain kernel:
the existing dependency
chain (in reverse order) is:
joulu 22 18:26:51 localhost.localdomain kernel:
-> #1
(&mm->mmap_sem){++++++}:
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff810bb386>] __lock_acquire+0x3d6/0xc40
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff810bbca0>] lock_acquire+0xb0/0x150
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff81181f3c>] might_fault+0x8c/0xb0
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffffa06c3055>] video_usercopy+0x355/0x4e0 [videodev]
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffffa06c31f5>] video_ioctl2+0x15/0x20 [videodev]
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffffa06bce73>] v4l2_ioctl+0x153/0x240 [videodev]
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff811e0590>] do_vfs_ioctl+0x300/0x520
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff811e0831>] SyS_ioctl+0x81/0xa0
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff816ca729>] system_call_fastpath+0x16/0x1b
joulu 22 18:26:51 localhost.localdomain kernel:
-> #0
(&dev->mutex#2){+.+.+.}:
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff810b96b7>] validate_chain.isra.36+0x10d7/0x1130
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff810bb386>] __lock_acquire+0x3d6/0xc40
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff810bbca0>] lock_acquire+0xb0/0x150
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff816bf1c7>] mutex_lock_interruptible_nested+0x77/0x460
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffffa073fde3>] vb2_fop_mmap+0x33/0x90 [videobuf2_core]
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffffa06bc85a>] v4l2_mmap+0x5a/0xa0 [videodev]
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff8118da7d>] mmap_region+0x3cd/0x5a0
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff8118dfa7>] do_mmap_pgoff+0x357/0x3e0
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff81178280>] vm_mmap_pgoff+0x90/0xc0
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff8118c553>] SyS_mmap_pgoff+0x1d3/0x270
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff810191a2>] SyS_mmap+0x22/0x30
joulu 22 18:26:51 localhost.localdomain kernel:
[<ffffffff816ca729>] system_call_fastpath+0x16/0x1b
joulu 22 18:26:51 localhost.localdomain kernel:
other info that might
help us debug this:
joulu 22 18:26:51 localhost.localdomain kernel: Possible unsafe locking
scenario:
joulu 22 18:26:51 localhost.localdomain kernel: CPU0
CPU1
joulu 22 18:26:51 localhost.localdomain kernel: ----
----
joulu 22 18:26:51 localhost.localdomain kernel: lock(&mm->mmap_sem);
joulu 22 18:26:51 localhost.localdomain kernel:
lock(&dev->mutex#2);
joulu 22 18:26:51 localhost.localdomain kernel:
lock(&mm->mmap_sem);
joulu 22 18:26:51 localhost.localdomain kernel: lock(&dev->mutex#2);
joulu 22 18:26:51 localhost.localdomain kernel:
*** DEADLOCK ***
joulu 22 18:26:51 localhost.localdomain kernel: 1 lock held by
video_source:sr/32072:
joulu 22 18:26:51 localhost.localdomain kernel: #0:
(&mm->mmap_sem){++++++}, at: [<ffffffff8117825f>] vm_mmap_pgoff+0x6f/0xc0
joulu 22 18:26:51 localhost.localdomain kernel:
stack backtrace:
joulu 22 18:26:51 localhost.localdomain kernel: CPU: 2 PID: 32072 Comm:
video_source:sr Tainted: G C O 3.13.0-rc1+ #77
joulu 22 18:26:51 localhost.localdomain kernel: Hardware name: System
manufacturer System Product Name/M5A78L-M/USB3, BIOS 1503 11/14/2012
joulu 22 18:26:51 localhost.localdomain kernel: ffffffff824fe950
ffff880283683b68 ffffffff816b8da9 ffffffff824fe950
joulu 22 18:26:51 localhost.localdomain kernel: ffff880283683ba8
ffffffff816b2c9b ffff880283683be0 0000000000000000
joulu 22 18:26:51 localhost.localdomain kernel: ffff88030637c378
0000000000000001 ffff88030637bcf0 ffff88030637c378
joulu 22 18:26:51 localhost.localdomain kernel: Call Trace:
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff816b8da9>]
dump_stack+0x4d/0x66
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff816b2c9b>]
print_circular_bug+0x200/0x20e
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff810b96b7>]
validate_chain.isra.36+0x10d7/0x1130
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff810bb3a7>] ?
__lock_acquire+0x3f7/0xc40
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff8101c413>] ?
native_sched_clock+0x13/0x80
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff810bb386>]
__lock_acquire+0x3d6/0xc40
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff8101c413>] ?
native_sched_clock+0x13/0x80
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff8101c489>] ?
sched_clock+0x9/0x10
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff810bbca0>]
lock_acquire+0xb0/0x150
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffffa073fde3>] ?
vb2_fop_mmap+0x33/0x90 [videobuf2_core]
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff816bf1c7>]
mutex_lock_interruptible_nested+0x77/0x460
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffffa073fde3>] ?
vb2_fop_mmap+0x33/0x90 [videobuf2_core]
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffffa073fde3>] ?
vb2_fop_mmap+0x33/0x90 [videobuf2_core]
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffffa073fde3>]
vb2_fop_mmap+0x33/0x90 [videobuf2_core]
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffffa06bc85a>]
v4l2_mmap+0x5a/0xa0 [videodev]
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff8118da7d>]
mmap_region+0x3cd/0x5a0
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff8118dfa7>]
do_mmap_pgoff+0x357/0x3e0
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff81178280>]
vm_mmap_pgoff+0x90/0xc0
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff8118c553>]
SyS_mmap_pgoff+0x1d3/0x270
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff810191a2>]
SyS_mmap+0x22/0x30
joulu 22 18:26:51 localhost.localdomain kernel: [<ffffffff816ca729>]
system_call_fastpath+0x16/0x1b
***********************************************
MSi3101 driver
***********************************************
joulu 22 00:30:39 localhost.localdomain kernel: usb 2-2:
msi3101_queue_setup: nbuffers=32 sizes[0]=8192
joulu 22 00:30:39 localhost.localdomain kernel: joulu 22 00:30:39
localhost.localdomain kernel:
======================================================
joulu 22 00:30:39 localhost.localdomain kernel: [ INFO: possible
circular locking dependency detected ]
joulu 22 00:30:39 localhost.localdomain kernel: 3.13.0-rc1+ #77 Tainted:
G C O
joulu 22 00:30:39 localhost.localdomain kernel:
-------------------------------------------------------
joulu 22 00:30:39 localhost.localdomain kernel: python/19615 is trying
to acquire lock:
joulu 22 00:30:39 localhost.localdomain kernel:
(&s->vb_queue_lock){+.+.+.}, at: [<ffffffffa06dade3>]
vb2_fop_mmap+0x33/0x90 [videobuf2_core]
joulu 22 00:30:39 localhost.localdomain kernel:
but task is already
holding lock:
joulu 22 00:30:39 localhost.localdomain kernel:
(&mm->mmap_sem){++++++}, at: [<ffffffff8117825f>] vm_mmap_pgoff+0x6f/0xc0
joulu 22 00:30:39 localhost.localdomain kernel:
which lock already
depends on the new lock.
joulu 22 00:30:39 localhost.localdomain kernel:
the existing dependency
chain (in reverse order) is:
joulu 22 00:30:39 localhost.localdomain kernel:
-> #1
(&mm->mmap_sem){++++++}:
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff810bb386>] __lock_acquire+0x3d6/0xc40
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff810bbca0>] lock_acquire+0xb0/0x150
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff81181f3c>] might_fault+0x8c/0xb0
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffffa06b3dba>] video_usercopy+0xba/0x4e0 [videodev]
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffffa06b41f5>] video_ioctl2+0x15/0x20 [videodev]
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffffa06ade73>] v4l2_ioctl+0x153/0x240 [videodev]
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff811e0590>] do_vfs_ioctl+0x300/0x520
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff811e0831>] SyS_ioctl+0x81/0xa0
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff816ca729>] system_call_fastpath+0x16/0x1b
joulu 22 00:30:39 localhost.localdomain kernel:
-> #0
(&s->vb_queue_lock){+.+.+.}:
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff810b96b7>] validate_chain.isra.36+0x10d7/0x1130
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff810bb386>] __lock_acquire+0x3d6/0xc40
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff810bbca0>] lock_acquire+0xb0/0x150
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff816bf1c7>] mutex_lock_interruptible_nested+0x77/0x460
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffffa06dade3>] vb2_fop_mmap+0x33/0x90 [videobuf2_core]
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffffa06ad85a>] v4l2_mmap+0x5a/0xa0 [videodev]
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff8118da7d>] mmap_region+0x3cd/0x5a0
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff8118dfa7>] do_mmap_pgoff+0x357/0x3e0
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff81178280>] vm_mmap_pgoff+0x90/0xc0
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff8118c553>] SyS_mmap_pgoff+0x1d3/0x270
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff810191a2>] SyS_mmap+0x22/0x30
joulu 22 00:30:39 localhost.localdomain kernel:
[<ffffffff816ca729>] system_call_fastpath+0x16/0x1b
joulu 22 00:30:39 localhost.localdomain kernel:
other info that might
help us debug this:
joulu 22 00:30:39 localhost.localdomain kernel: Possible unsafe locking
scenario:
joulu 22 00:30:39 localhost.localdomain kernel: CPU0
CPU1
joulu 22 00:30:39 localhost.localdomain kernel: ----
----
joulu 22 00:30:39 localhost.localdomain kernel: lock(&mm->mmap_sem);
joulu 22 00:30:39 localhost.localdomain kernel:
lock(&s->vb_queue_lock);
joulu 22 00:30:39 localhost.localdomain kernel:
lock(&mm->mmap_sem);
joulu 22 00:30:39 localhost.localdomain kernel: lock(&s->vb_queue_lock);
joulu 22 00:30:39 localhost.localdomain kernel:
*** DEADLOCK ***
joulu 22 00:30:39 localhost.localdomain kernel: 1 lock held by python/19615:
joulu 22 00:30:39 localhost.localdomain kernel: #0:
(&mm->mmap_sem){++++++}, at: [<ffffffff8117825f>] vm_mmap_pgoff+0x6f/0xc0
joulu 22 00:30:39 localhost.localdomain kernel:
stack backtrace:
joulu 22 00:30:39 localhost.localdomain kernel: CPU: 2 PID: 19615 Comm:
python Tainted: G C O 3.13.0-rc1+ #77
joulu 22 00:30:39 localhost.localdomain kernel: Hardware name: System
manufacturer System Product Name/M5A78L-M/USB3, BIOS 1503 11/14/2012
joulu 22 00:30:39 localhost.localdomain kernel: ffffffff825038c0
ffff8802028ffb68 ffffffff816b8da9 ffffffff825038c0
joulu 22 00:30:39 localhost.localdomain kernel: ffff8802028ffba8
ffffffff816b2c9b ffff8802028ffbe0 0000000000000000
joulu 22 00:30:39 localhost.localdomain kernel: ffff880202bcec18
0000000000000001 ffff880202bce590 ffff880202bcec18
joulu 22 00:30:39 localhost.localdomain kernel: Call Trace:
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff816b8da9>]
dump_stack+0x4d/0x66
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff816b2c9b>]
print_circular_bug+0x200/0x20e
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff810b96b7>]
validate_chain.isra.36+0x10d7/0x1130
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff810bb3a7>] ?
__lock_acquire+0x3f7/0xc40
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff8101c413>] ?
native_sched_clock+0x13/0x80
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff810bb386>]
__lock_acquire+0x3d6/0xc40
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff81182706>] ?
__do_fault+0x236/0x510
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff8101c413>] ?
native_sched_clock+0x13/0x80
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff8101c489>] ?
sched_clock+0x9/0x10
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff810bbca0>]
lock_acquire+0xb0/0x150
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffffa06dade3>] ?
vb2_fop_mmap+0x33/0x90 [videobuf2_core]
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff816bf1c7>]
mutex_lock_interruptible_nested+0x77/0x460
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffffa06dade3>] ?
vb2_fop_mmap+0x33/0x90 [videobuf2_core]
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffffa06dade3>] ?
vb2_fop_mmap+0x33/0x90 [videobuf2_core]
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffffa06dade3>]
vb2_fop_mmap+0x33/0x90 [videobuf2_core]
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffffa06ad85a>]
v4l2_mmap+0x5a/0xa0 [videodev]
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff8118da7d>]
mmap_region+0x3cd/0x5a0
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff8118dfa7>]
do_mmap_pgoff+0x357/0x3e0
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff81178280>]
vm_mmap_pgoff+0x90/0xc0
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff8118c553>]
SyS_mmap_pgoff+0x1d3/0x270
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff810191a2>]
SyS_mmap+0x22/0x30
joulu 22 00:30:39 localhost.localdomain kernel: [<ffffffff816ca729>]
system_call_fastpath+0x16/0x1b
joulu 22 00:30:39 localhost.localdomain kernel: usb 2-2:
msi3101_start_streaming:
joulu 22 00:30:39 localhost.localdomain kernel: usb 2-2:
msi3101_set_usb_adc: div_r_out=4 f_vco=0
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