Re: [Xen-devel] xen pci passthrough hung task instead of terminate

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Sun, Jul 25, 2010 at 05:35:07PM +0200, Sander Eikelenboom wrote:
> Hi Konrad,
> 
> I have tried both your trees, together with some experimental usb3 stuff.

How many CPUs do you have assigned to your guest?

I presume this problem does not appear under baremetal? Thought
looking at the stack I would think it would too - it does not
look Xen specific - just that a mutex is deadlocked.

> It seems to work apart from some usb3 problems after several hours of 
> videograbbing, in the end it crashes the program, but instead of terminating 
> it keeps hanging.
> Since xen_evtchn is on the trace stack i'm wondering if any xen parts are 
> causing it to hang instead of terminate.

Here is what the mutex_lock says:

 71 /***
 72  * mutex_lock - acquire the mutex
 73  * @lock: the mutex to be acquired
 74  *
 75  * Lock the mutex exclusively for this task. If the mutex is not
 76  * available right now, it will sleep until it can get it.
 77  *
 78  * The mutex must later on be released by the same task that
 79  * acquired it. Recursive locking is not allowed. The task
 80  * may not exit without first unlocking the mutex. Also, kernel
 81  * memory where the mutex resides mutex must not be freed with
 82  * the mutex still locked. The mutex must first be initialized
 83  * (or statically defined) before it can be locked. memset()-ing
 84  * the mutex to 0 is not allowed.
 85  *
 86  * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
 87  *   checks that will enforce the restrictions and will also do
 88  *   deadlock debugging. )
 89  *
 90  * This function is similar to (but not equivalent to) down()

So I think the next step is to try CONFIG_DEBUG_MUTEXES, and see
what it tells you.

> 
> --
> Sander
> 
> 
> 
> Jul 25 16:54:26 security kernel: [26400.136170] "echo 0 > 
> /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> Jul 25 16:54:26 security kernel: [26400.136191] motion        D 
> ffffffff810049f9     0  1556      1 0x00000000
> Jul 25 16:54:26 security kernel: [26400.136220]  ffff88001fce6800 
> 0000000000000286 0000000000000001 0000000000014580
> Jul 25 16:54:26 security kernel: [26400.136254]  ffff88001e251fd8 
> ffff88001e251fd8 ffff88001e088100 0000000000014580
> Jul 25 16:54:26 security kernel: [26400.136285]  0000000000014580 
> 0000000000014580 ffff88001e088100 0000000000000001
> Jul 25 16:54:26 security kernel: [26400.136316] Call Trace:
> Jul 25 16:54:26 security kernel: [26400.136346]  [<ffffffff8142c33c>] ? 
> __mutex_lock_slowpath+0xda/0x125
> Jul 25 16:54:26 security kernel: [26400.136374]  [<ffffffff8142c1e1>] ? 
> mutex_lock+0x12/0x28
> Jul 25 16:54:26 security kernel: [26400.136399]  [<ffffffffa0015ea5>] ? 
> videobuf_streamoff+0x13/0x34 [videobuf_core]
> Jul 25 16:54:26 security kernel: [26400.136424]  [<ffffffff81005cc5>] ? 
> xen_force_evtchn_callback+0x9/0xa
> Jul 25 16:54:26 security kernel: [26400.136449]  [<ffffffffa008b5a8>] ? 
> vidioc_streamoff+0x7e/0xb5 [em28xx]
> Jul 25 16:54:26 security kernel: [26400.136473]  [<ffffffffa00355fe>] ? 
> __video_do_ioctl+0x181f/0x3cc7 [videodev]
> Jul 25 16:54:26 security kernel: [26400.136496]  [<ffffffff8100631f>] ? 
> xen_restore_fl_direct_end+0x0/0x1
> Jul 25 16:54:26 security kernel: [26400.136517]  [<ffffffff8142d2a4>] ? 
> _raw_spin_unlock_irqrestore+0xc/0xd
> Jul 25 16:54:26 security kernel: [26400.136539]  [<ffffffff81393cda>] ? 
> sock_def_readable+0x3b/0x5d
> Jul 25 16:54:26 security kernel: [26400.136561]  [<ffffffff81404296>] ? 
> unix_dgram_sendmsg+0x428/0x4b2
> Jul 25 16:54:26 security kernel: [26400.136580]  [<ffffffff810058fa>] ? 
> xen_set_pte_at+0x196/0x1b6
> Jul 25 16:54:26 security kernel: [26400.136600]  [<ffffffff810036bd>] ? 
> __raw_callee_save_xen_make_pte+0x11/0x1e
> Jul 25 16:54:26 security kernel: [26400.136620]  [<ffffffff81390c1e>] ? 
> sock_sendmsg+0xd1/0xec
> Jul 25 16:54:26 security kernel: [26400.136641]  [<ffffffff810b117c>] ? 
> __do_fault+0x3eb/0x426
> Jul 25 16:54:26 security kernel: [26400.136662]  [<ffffffffa0037d38>] ? 
> video_ioctl2+0x292/0x32e [videodev]
> Jul 25 16:54:26 security kernel: [26400.136684]  [<ffffffff8139271a>] ? 
> sys_sendto+0x10d/0x127
> Jul 25 16:54:26 security kernel: [26400.136702]  [<ffffffff81006332>] ? 
> check_events+0x12/0x20
> Jul 25 16:54:26 security kernel: [26400.136722]  [<ffffffffa003310b>] ? 
> v4l2_ioctl+0x38/0x3a [videodev]
> Jul 25 16:54:26 security kernel: [26400.136742]  [<ffffffff810d45be>] ? 
> vfs_ioctl+0x69/0x92
> Jul 25 16:54:26 security kernel: [26400.136760]  [<ffffffff810d4a6e>] ? 
> do_vfs_ioctl+0x411/0x43c
> Jul 25 16:54:26 security kernel: [26400.136779]  [<ffffffff810c874c>] ? 
> vfs_write+0x134/0x169
> Jul 25 16:54:26 security kernel: [26400.136797]  [<ffffffff810d4aea>] ? 
> sys_ioctl+0x51/0x70
> Jul 25 16:54:26 security kernel: [26400.136815]  [<ffffffff810086c2>] ? 
> system_call_fastpath+0x16/0x1b
> 
> 
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