Hello,
my kernel is a bit unhappy with lock ordering between mm->mmap_sem
and videobuf_queue->lock.
Thanks,
Petr Vandrovec
=======================================================
[ INFO: possible circular locking dependency detected ]
-------------------------------------------------------
mythbackend/8289 is trying to acquire lock:
(&mm->mmap_sem){----}, at: [<ffffffff881d2ad5>] videobuf_dma_init_user+0xd5/0x190 [video_buf]
but task is already holding lock:
(&q->lock#2){--..}, at: [<ffffffff81072905>] mutex_lock+0x25/0x30
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&q->lock#2){--..}:
[<ffffffff810bacbe>] lock_acquire+0x4e/0x70
[<ffffffff81072746>] __mutex_lock_slowpath+0xd6/0x270
[<ffffffff81072904>] mutex_lock+0x24/0x30
[<ffffffff881d192b>] videobuf_mmap_mapper+0x1b/0x290 [video_buf]
[<ffffffff881dc9bc>] bttv_mmap+0x5c/0x70 [bttv]
[<ffffffff8100e927>] do_mmap_pgoff+0x4f7/0x7d0
[<ffffffff810924eb>] sys32_mmap2+0xbb/0xf0
[<ffffffff8106f69f>] cstar_do_call+0x1a/0x6f
-> #0 (&mm->mmap_sem){----}:
[<ffffffff810bacbe>] lock_acquire+0x4e/0x70
[<ffffffff810b74c8>] down_read+0x38/0x50
[<ffffffff881d2ad4>] videobuf_dma_init_user+0xd4/0x190 [video_buf]
[<ffffffff881d2eab>] videobuf_iolock+0xab/0x120 [video_buf]
[<ffffffff881dc8b8>] bttv_prepare_buffer+0x158/0x1c0 [bttv]
[<ffffffff881de8ce>] bttv_do_ioctl+0xbfe/0x20e0 [bttv]
[<ffffffff88175f98>] video_usercopy+0x188/0x250 [videodev]
[<ffffffff881dca7b>] bttv_ioctl+0x3b/0x50 [bttv]
[<ffffffff881bd064>] native_ioctl+0x64/0x90 [compat_ioctl32]
[<ffffffff881bebfc>] v4l_compat_ioctl32+0x1b6c/0x1c2c [compat_ioctl32]
[<ffffffff8110906a>] compat_sys_ioctl+0xfa/0x330
[<ffffffff8106f69f>] cstar_do_call+0x1a/0x6f
other info that might help us debug this:
1 lock held by mythbackend/8289:
#0: (&q->lock#2){--..}, at: [<ffffffff81072905>] mutex_lock+0x25/0x30
stack backtrace:
Call Trace:
[<ffffffff8107bd05>] show_trace+0xb5/0x3a0
[<ffffffff8107c005>] dump_stack+0x15/0x20
[<ffffffff810b8ed2>] print_circular_bug_tail+0x72/0x80
[<ffffffff810ba93e>] __lock_acquire+0x9ae/0xce0
[<ffffffff810bacbf>] lock_acquire+0x4f/0x70
[<ffffffff810b74c9>] down_read+0x39/0x50
[<ffffffff881d2ad5>] :video_buf:videobuf_dma_init_user+0xd5/0x190
[<ffffffff881d2eac>] :video_buf:videobuf_iolock+0xac/0x120
[<ffffffff881dc8b9>] :bttv:bttv_prepare_buffer+0x159/0x1c0
[<ffffffff881de8cf>] :bttv:bttv_do_ioctl+0xbff/0x20e0
[<ffffffff88175f99>] :videodev:video_usercopy+0x189/0x250
[<ffffffff881dca7c>] :bttv:bttv_ioctl+0x3c/0x50
[<ffffffff881bd065>] :compat_ioctl32:native_ioctl+0x65/0x90
[<ffffffff881bebfd>] :compat_ioctl32:v4l_compat_ioctl32+0x1b6d/0x1c2c
[<ffffffff8110906b>] compat_sys_ioctl+0xfb/0x330
[<ffffffff8106f6a0>] cstar_do_call+0x1b/0x6f
[<00000000ffffe405>]
On Sun, 2006-08-20 at 21:19 +0200, Petr Vandrovec wrote:
> Hello,
> my kernel is a bit unhappy with lock ordering between mm->mmap_sem
> and videobuf_queue->lock.
> Thanks,
> Petr Vandrovec
looks like a real deadlock to me...
bttv_prepare_buffer takes mutex then
videobuf_dma_init_user takes mmap_sem
do_mmap_pgoff takes mmap_sem then calls
bttv_mmap which calls
videobuf_mmap_mapper takes the mutex
so a classic AB-BA deadlock....