linux-kernel - Re: Kaffeine problem with CFS

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Message-ID: <20070418104955.GB2673@elte.hu>
Date:	Wed, 18 Apr 2007 12:49:55 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Pfister <christophpfister@...il.com>
Cc:	S.Çağlar Onur <caglar@...dus.org.tr>,
	linux-kernel@...r.kernel.org,
	Michael Lothian <mike@...eburn.co.uk>,
	Christophe Thommeret <hftom@...e.fr>,
	Jurgen Kofler <kaffeine@....net>,
	Ulrich Drepper <drepper@...hat.com>
Subject: Re: Kaffeine problem with CFS


* Ingo Molnar <mingo@...e.hu> wrote:

> > hm. I've reviewed all uses of demux_lock. ./src/xine-engine/demux.c 
> > does this:
> 
> plus it does this too:
> 
>       pthread_mutex_unlock( &stream->demux_lock );
>       xine_usec_sleep(100000);
>       pthread_mutex_lock( &stream->demux_lock );
> 
> this would explain the nanosleep() strace entries. But the task stuck 
> on demux_lock never gets the unlock event. Weird.

9303 is stuck here on demux_lock:

#0  0xffffe410 in __kernel_vsyscall ()
#1  0x4a2538ce in __lll_mutex_lock_wait () from /lib/libpthread.so.0
#2  0x4a24f71c in _L_mutex_lock_79 () from /lib/libpthread.so.0
#3  0x4a24f24d in pthread_mutex_lock () from /lib/libpthread.so.0
#4  0xb79f64f9 in xine_play () from /usr/lib/libxine.so.1

that mutex related futex is at address 0xb07409e0, but the only sign in 
the strace of that futex being touched is:

9303  futex(0xb07409e0, FUTEX_WAIT, 2, NULL <unfinished ...>

no other event ever happens on futex 0xb07409e0. Other threads dont 
touch it.

Maybe thread 9324 is the owner of that mutex, and it's looping somewhere 
that does xine_xmalloc_aligned(), with the lock held? It did this:

#0  0xffffe410 in __kernel_vsyscall ()
#1  0x4a2539e1 in __lll_mutex_unlock_wake () from /lib/libpthread.so.0
#2  0x4a2506f9 in _L_mutex_unlock_99 () from /lib/libpthread.so.0
#3  0x4a250370 in __pthread_mutex_unlock_usercnt () from /lib/libpthread.so.0
#4  0x4a2506f0 in pthread_mutex_unlock () from /lib/libpthread.so.0
#5  0xb79fce5a in QWidget::setUpdatesEnabled () from /usr/lib/libxine.so.1
#6  0xb7a4b90b in dvd_plugin_free_buffer (buf=0xb0745470) at input_dvd.c:570
#7  0xb7a030a2 in QWidget::setUpdatesEnabled () from /usr/lib/libxine.so.1
#8  0x4a24d2db in start_thread () from /lib/libpthread.so.0
#9  0x4a05820e in clone () from /lib/libc.so.6

	Ingo
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