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SubjectRe: [linux-dvb] cx88-blackbird broken (since 2.6.37)
Hi Andi,

Huber Andreas wrote[1]:

> [Symptom]
> Processes that try to open a cx88-blackbird driven MPEG device will hang up.

Thanks for reporting. Just cc-ing some relevant people. Could you file a
bug to track this at <http://bugzilla.kernel.org/>, product v4l-dvb,
component cx88, and then send the bug number to 619827@bugs.debian.org ?

Report follows.

Jonathan

[1] http://bugs.debian.org/619827

> [Cause]
> Nestet mutex_locks (which are not allowed) result in a deadlock.
>
> [Details]
> Source-File: drivers/media/video/cx88/cx88-blackbird.c
> Function: int mpeg_open(struct file *file)
> Problem: the calls to drv->request_acquire(drv); and
> drv->request_release(drv); will hang because they try to lock a
> mutex that has already been locked by a previouse call to
> mutex_lock(&dev->core->lock) ...
>
> 1050 static int mpeg_open(struct file *file)
> 1051 {
> [...]
> 1060 mutex_lock(&dev->core->lock); // MUTEX LOCKED !!!!!!!!!!!!!!!!
> 1061
> 1062 /* Make sure we can acquire the hardware */
> 1063 drv = cx8802_get_driver(dev, CX88_MPEG_BLACKBIRD);
> 1064 if (drv) {
> 1065 err = drv->request_acquire(drv); // HANGS !!!!!!!!!!!!!!!!!!!
> 1066 if(err != 0) {
> 1067 dprintk(1,"%s: Unable to acquire hardware, %d\n", __func__, err);
> 1068 mutex_unlock(&dev->core->lock);;
> 1069 return err;
> 1070 }
> 1071 }
> [...]
>
> Here's the relevant kernel log extract (Linux version 2.6.38-1-amd64 (Debian 2.6.38-1)) ...
>
> Mar 24 21:25:10 xen kernel: [ 241.472067] INFO: task v4l_id:1000 blocked for more than 120 seconds.
> Mar 24 21:25:10 xen kernel: [ 241.478845] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> Mar 24 21:25:10 xen kernel: [ 241.482412] v4l_id D ffff88006bcb6540 0 1000 1 0x00000000
> Mar 24 21:25:10 xen kernel: [ 241.486031] ffff88006bcb6540 0000000000000086 ffff880000000001 ffff88006981c380
> Mar 24 21:25:10 xen kernel: [ 241.489694] 0000000000013700 ffff88006be5bfd8 ffff88006be5bfd8 0000000000013700
> Mar 24 21:25:10 xen kernel: [ 241.493301] ffff88006bcb6540 ffff88006be5a010 ffff88006bcb6540 000000016be5a000
> Mar 24 21:25:10 xen kernel: [ 241.496766] Call Trace:
> Mar 24 21:25:10 xen kernel: [ 241.500145] [<ffffffff81321c4a>] ? __mutex_lock_common+0x127/0x193
> Mar 24 21:25:10 xen kernel: [ 241.503630] [<ffffffff81321d82>] ? mutex_lock+0x1a/0x33
> Mar 24 21:25:10 xen kernel: [ 241.507145] [<ffffffffa09dd155>] ? cx8802_request_acquire+0x66/0xc6 [cx8802]
> Mar 24 21:25:10 xen kernel: [ 241.510699] [<ffffffffa0aab7f2>] ? mpeg_open+0x7a/0x1fc [cx88_blackbird]
> Mar 24 21:25:10 xen kernel: [ 241.514279] [<ffffffff8123bfb6>] ? kobj_lookup+0x139/0x173
> Mar 24 21:25:10 xen kernel: [ 241.517856] [<ffffffffa062d5fd>] ? v4l2_open+0xb3/0xdf [videodev]


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