Re: mISDN_send: error -12 strikes again

On Sun, Mar 18, 2012 at 07:29:08AM +0100, jolly wrote:
> Ralf Schlatterbeck wrote:
> > Yesterday we had the message "mISDN_send: error -12" filling
> > /var/log/kern.log. Restarting asterisk "fixed" it.
> >
> >   
> hi ralf,
> 
> i guess it is because chan_lcr runs into deadlock inside asterisk. since
> the process of chan_lcr holds a lock and never returns after calling
> some asterisk function, bchannel read will not be processed, so the
> kernel drops messages to prevent overfill. this is why you receive the
> message above.

Yes, I've debugged this once and am following that bug for some time
now... the kernel message simply indicates that we have a buffer
overflow in kernel space, nobody is fetching the data.

> i suggest do debug which process calls the chan_lcr global lock and
> unlock function. then, if asterisk hangs, use gdb to do backtrace all
> threads of asterisk. you can see against which lock each thread runs.
> since locking mechanism of asterisk is quite complex and unknown to me,
> you might be on your own with that.

I've looked through the locking code and have some questions:
- There is an LCR thread in chan_lcr
- no other threads are explicitly created, I guess asterisk will call
  the lcr-provided routines from different threads, is this right?
- I don't understand why in lcr_hangup the lock is only obtained if the
  thread is different from the lcr thread.

so when instrumenting the code, I have to deal with the case that we
have several threads calling the various routines of chan_lcr?

Ralf
-- 
Ralf Schlatterbeck             email: [email protected]