[Mesa3d-dev] Bug in mesa-master: Deadlock for multi-threaded glx apps inside __glXInitialize()

Sun, 01 Aug 2010 20:20:25 -0700 

Think i sent it to the wrong mailing list. Here we go again...

Begin forwarded message:


From: Mario Kleiner <mario.klei...@tuebingen.mpg.de>
Date: July 27, 2010 2:56:04 AM GMT+02:00
To: Kristian Hogsberg <k...@bitplanet.net>, xorg-de...@lists.x.org
Subject: Bug: Deadlock for multi-threaded glx apps inside __glXInitialize() 

Hi Kristian
Testing with current mesa master, my toolkit deadlocks on the first call to a glX function (glXChooseVisual()). 

The deadlock was probably introduced by your recent commit:

"glx: Use _Xglobal_lock for protecting extension display list"

ab434f6b7641a64d30725a9ac24929240362d466
The problem is that the _Xglobal_lock is locked twice inside the __glXInitialize() function of mesa/src/glx/glxext.c, once inside __glXInitialize(), and then as part of dri2CreateDisplay() -> ... - > XextFindDisplay. The 2nd locking call on the already held lock deadlocks.
Attached a backtrace with the problem and a patch/hack that "fixes" it for me, but introduces a race-condition itself, so this is obviously not the correct solution. The race condition would trigger if two threads would simultaneously do their first call to a glX function for the same Display* dpy handle, rather unlikely to happen in practice? If so, then the patch might be an acceptable fix until a better solution is found?
Other applications (glxgears, games etc.) work correctly. The difference is that my toolkit calls XInitThreads() at startup to use xlib multi-threaded and afaik the locking calls only get enabled if xlib is switched to thread-safe mode, otherwise they are no-ops? If i omit XInitThreads() everything works again. 

thanks,
-mario

Attachment: 0001-mesa-glx-Work-around-deadlock-on-_Xglobal_lock-in-__.patch
Description: Binary data

#0  0x0012d422 in __kernel_vsyscall ()
#1  0x031ccaf9 in __lll_lock_wait () from /lib/tls/i686/cmov/libpthread.so.0
#2  0x031c813b in _L_lock_748 () from /lib/tls/i686/cmov/libpthread.so.0
#3  0x031c7f61 in pthread_mutex_lock () from /lib/tls/i686/cmov/libpthread.so.0
#4  0x0310fba6 in pthread_mutex_lock () from /lib/tls/i686/cmov/libc.so.6
#5  0x0292f41f in _XLockMutex (lip=0x2a25e34) at ../../src/locking.c:107
#6  0x034729af in XextFindDisplay (extinfo=0x0, dpy=0x84debb0) at 
../../src/extutil.c:232
#7  0x0344faff in DRI2FindDisplay (dpy=0x84debf0) at dri2.c:81
#8  0x0344fd6e in DRI2QueryExtension (dpy=0x84debf0, eventBase=0xbfffd9cc, 
errorBase=0xbfffd9c8) at dri2.c:184
#9  0x0344e653 in dri2CreateDisplay (dpy=0x84debf0) at dri2_glx.c:900
#10 0x0342a6ce in __glXInitialize (dpy=0x84debf0) at glxext.c:848
#11 0x0342764a in GetGLXPrivScreenConfig (dpy=0x84debf0, scrn=0, 
ppriv=0xbfffdbdc, ppsc=0xbfffdbd8) at glxcmds.c:183
#12 0x03427d46 in glXChooseVisual (dpy=0x84debf0, screen=0, 
attribList=0xbfffdcd8) at glxcmds.c:1495
#13 0x032dae3f in PsychOSOpenOnscreenWindow (screenSettings=0xbfffe114, 
windowRecord=0x8501010, numBuffers=2, stereomode=0, 
    conserveVRAM=0) at Linux/Screen/PsychWindowGlue.c:288
#14 0x032ee883 in PsychOpenOnscreenWindow (screenSettings=0xbfffe114, 
windowRecord=0xbfffe110, numBuffers=2, stereomode=0, 
    rect=0xbfffe1b0, multiSample=0, sharedContextWindow=0x0) at 
Common/Screen/PsychWindowSupport.c:295
#15 0x0330e57c in SCREENOpenWindow () at Common/Screen/SCREENOpenWindow.c:301
#16 0x0334b79b in mexFunction (nlhs=1, plhs=0xb5ee7018, nrhs=4, 
prhs=0xb5ee7008) at Common/Base/PsychScriptingGlue.cc:959
#17 0x004e0f25 in call_mex(bool, void*, octave_value_list const&, int, 
octave_mex_function*) ()
   from /usr/lib/octave-3.2.3/liboctinterp.so
#18 0x006f8868 in octave_mex_function::do_multi_index_op(int, octave_value_list 
const&) ()
   from /usr/lib/octave-3.2.3/liboctinterp.so



*********************************************************************
Mario Kleiner
Max Planck Institute for Biological Cybernetics
Spemannstr. 38
72076 Tuebingen
Germany

e-mail: mario.klei...@tuebingen.mpg.de
office: +49 (0)7071/601-1623
fax:    +49 (0)7071/601-616
www:    http://www.kyb.tuebingen.mpg.de/~kleinerm
*********************************************************************
"For a successful technology, reality must take precedence
over public relations, for Nature cannot be fooled."
(Richard Feynman)



*********************************************************************
Mario Kleiner
Max Planck Institute for Biological Cybernetics
Spemannstr. 38
72076 Tuebingen
Germany

e-mail: mario.klei...@tuebingen.mpg.de
office: +49 (0)7071/601-1623
fax:    +49 (0)7071/601-616
www:    http://www.kyb.tuebingen.mpg.de/~kleinerm
*********************************************************************
"For a successful technology, reality must take precedence
over public relations, for Nature cannot be fooled."
(Richard Feynman)


------------------------------------------------------------------------------
The Palm PDK Hot Apps Program offers developers who use the
Plug-In Development Kit to bring their C/C++ apps to Palm for a share
of $1 Million in cash or HP Products. Visit us here for more details:
http://p.sf.net/sfu/dev2dev-palm
_______________________________________________
Mesa3d-dev mailing list
Mesa3d-dev@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/mesa3d-dev

Reply via email to