[poppler] XRef::fetch mutex lock

Tue Apr 2 15:01:20 PDT 2013

El Dimarts, 2 d'abril de 2013, a les 10:36:53, Thomas Freitag va escriure:
> Am 02.04.2013 09:22, schrieb Thomas Freitag:
> > Hi Albert!
> > 
> > Am 27.03.2013 12:29, schrieb Thomas Freitag:
> >> Sorry, pushed the wrong button, here my answer to the list:
> >> 
> >> Am 27.03.2013 11:41, schrieb Albert Astals Cid:
> >>> Why do we pass around the recursion integer around?
> >> 
> >> No idea: The recursive integer wasn't introduced by the thread safe
> >> patch, it was already there. I just used it and extend some functions
> >> which incorrectly ignore that parameter instead of passing it to the
> >> called functions. Probably I missed some more than only the one in
> >> DCTStream::DCTStream.
> > 
> > I just ran a regression test over my PDF files, but I didn't get any
> > dead locks. So if You want me to solve that problem, You should
> > provide me that PDF. (Regardless if You prefer to use recursive mutex:
> > the endless loop detection need to pass the recursive integer
> > everywhere!)
> 
> Attached a patch which corrects it. I made it in my sleep, 'cause the
> dead lock was probably caused by my patch for bug 61994 (even if that
> PDF doesn't cause any dead locks). This time I also respect the
> DCTStream usage if LIBJPEG is disabled :-)

Sure, this fixes the issue (and we should commit it to help with the infinite 
recursion issue), but what's your opinion on making our mutexes recursive?

It should help us making the code simpler since we could just drop all the 
DoNotLockMutex cases, no?

Cheers,
  Albert

> 
> Cheers,
> Thomas
> 
> > Cheers,
> > Thomas
> > 
> >>> Wouldn't a real recursive mutex be enough?
> >> 
> >> No idea: I used in the thread safe patch just the pthread_lock which
> >> was defined. I'm not knowing what happens when we change it globally
> >> i.e. if it affects other usages of the GooMutex. Just feel free to
> >> change it, You should have the better overview of usages than I have.
> >> 
> >> Cheers,
> >> Thomas
> >> 
> >>> I'm asking because i have a document here (that sadly i can't share)
> >>> that is deadlocking
> >>> itself there because we are not passing the recursion integer
> >>> everywhere (we lose it in DCTStream::DCTStream)
> >>> as shown in this backtrace
> >>> 
> >>> #0  __lll_lock_wait () at
> >>> ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135
> >>> #1  0x00007ffff599217c in _L_lock_982 () from
> >>> /lib/x86_64-linux-gnu/libpthread.so.0
> >>> #2  0x00007ffff5991fcb in __GI___pthread_mutex_lock (mutex=0x71dc10)
> >>> at pthread_mutex_lock.c:64
> >>> #3  0x00007ffff5f02f73 in MutexLocker::MutexLocker
> >>> (this=0x7fffffffcfb0, mutexA=0x71dc10, modeA=DoLockMutex) at
> >>> /home/tsdgeos/devel/poppler/goo/GooMutex.h:72
> >>> #4  0x00007ffff5fac8e2 in XRef::fetch (this=0x71db50, num=5, gen=0,
> >>> obj=0x7fffffffd0b0, recursion=0) at
> >>> /home/tsdgeos/devel/poppler/poppler/XRef.cc:1137
> >>> #5  0x00007ffff5f8a013 in Object::fetch (this=0x71fe08,
> >>> xref=0x71db50, obj=0x7fffffffd0b0, recursion=0) at
> >>> /home/tsdgeos/devel/poppler/poppler/Object.cc:122
> >>> #6  0x00007ffff5f19de4 in Dict::lookup (this=0x71fb60,
> >>> key=0x7ffff606fbba "Height", obj=0x7fffffffd0b0, recursion=0) at
> >>> /home/tsdgeos/devel/poppler/poppler/Dict.cc:256
> >>> #7  0x00007ffff5f032e9 in Object::dictLookup (this=0x7fffffffd5a0,
> >>> key=0x7ffff606fbba "Height", obj=0x7fffffffd0b0, recursion=0) at
> >>> /home/tsdgeos/devel/poppler/poppler/Object.h:315
> >>> #8  0x00007ffff601f8a3 in DCTStream::DCTStream (this=0x7832b0,
> >>> strA=0x720780, colorXformA=-1, dict=0x7fffffffd5a0) at
> >>> /home/tsdgeos/devel/poppler/poppler/DCTStream.cc:72
> >>> #9  0x00007ffff5f9bf6d in Stream::makeFilter (this=0x720780,
> >>> name=0x71fef0 "DCTDecode", str=0x720780, params=0x7fffffffd1e0,
> >>> recursion=1, dict=0x7fffffffd5a0) at
> >>> /home/tsdgeos/devel/poppler/poppler/Stream.cc:311
> >>> #10 0x00007ffff5f9b71a in Stream::addFilters (this=0x720780,
> >>> dict=0x7fffffffd5a0, recursion=1) at
> >>> /home/tsdgeos/devel/poppler/poppler/Stream.cc:184
> >>> #11 0x00007ffff5f9204b in Parser::makeStream (this=0x71fcd0,
> >>> dict=0x7fffffffd5a0, fileKey=0x0, encAlgorithm=cryptRC4,
> >>> keyLength=1146103040, objNum=3, objGen=0, recursion=1, strict=false)
> >>> at /home/tsdgeos/devel/poppler/poppler/Parser.cc:280
> >>> #12 0x00007ffff5f918e6 in Parser::getObj (this=0x71fcd0,
> >>> obj=0x7fffffffd5a0, simpleOnly=false, fileKey=0x0,
> >>> encAlgorithm=cryptRC4, keyLength=1146103040, objNum=3, objGen=0,
> >>> recursion=0, strict=false) at
> >>> /home/tsdgeos/devel/poppler/poppler/Parser.cc:131
> >>> #13 0x00007ffff5facdd3 in XRef::fetch (this=0x71db50, num=3, gen=0,
> >>> obj=0x7fffffffd5a0, recursion=0) at
> >>> /home/tsdgeos/devel/poppler/poppler/XRef.cc:1197
> >>> #14 0x00007ffff5f8a013 in Object::fetch (this=0x71e128,
> >>> xref=0x71db50, obj=0x7fffffffd5a0, recursion=0) at
> >>> /home/tsdgeos/devel/poppler/poppler/Object.cc:122
> >>> #15 0x00007ffff5f19de4 in Dict::lookup (this=0x71e660, key=0x7206e0
> >>> "Im1", obj=0x7fffffffd5a0, recursion=0) at
> >>> /home/tsdgeos/devel/poppler/poppler/Dict.cc:256
> >>> #16 0x00007ffff5f032e9 in Object::dictLookup (this=0x71e598,
> >>> key=0x7206e0 "Im1", obj=0x7fffffffd5a0, recursion=0) at
> >>> /home/tsdgeos/devel/poppler/poppler/Object.h:315
> >>> #17 0x00007ffff5f2a647 in GfxResources::lookupXObject
> >>> (this=0x71e590, name=0x7206e0 "Im1", obj=0x7fffffffd5a0) at
> >>> /home/tsdgeos/devel/poppler/poppler/Gfx.cc:411
> >>> #18 0x00007ffff5f3f41e in Gfx::opXObject (this=0x71e440,
> >>> args=0x7fffffffd720, numArgs=1) at
> >>> /home/tsdgeos/devel/poppler/poppler/Gfx.cc:4114
> >>> #19 0x00007ffff5f2bfd6 in Gfx::execOp (this=0x71e440,
> >>> cmd=0x7fffffffd6e0, args=0x7fffffffd720, numArgs=1) at
> >>> /home/tsdgeos/devel/poppler/poppler/Gfx.cc:858
> >>> #20 0x00007ffff5f2b82b in Gfx::go (this=0x71e440, topLevel=true) at
> >>> /home/tsdgeos/devel/poppler/poppler/Gfx.cc:717
> >>> 
> >>> 
> >>> Cheers,
> >>> 
> >>>    Albert
> >>> 
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> >>> 
> >>> .
> >> 
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