Re: [Sablevm-developer] JGFSyncBench fails

[Chris P. <chr...@ma...>]

David B=E9langer wrote:

> Hi Chris,
>=20
> Did you ran it with --enable-debugging?
> Or at least without signals for execption?
>=20
> If not, run it without signals for exceptions.  (seg faults are
> interpreted as NullPointerEx).
>=20
> If it seg faults you can use gdb to find location.

Hi David,

My shell wasn't creating core files, and so I wasn't using gdb.=20
'ulimitb -c unlimited' fixed that.

It segfaults inside pthread_mutex_lock(), called when inflating a thin=20
lock, inside _svmf_enter_object_monitor(), called from INVOKEVIRTUAL
(the benchmark tests calling a synchronized method over and over).

I've read through all the locking stuff, but I can't see any errors in=20
the logic.  I was seeing similar things with mtrt and my spmt version:=20
there there was a concurrency error restoring the thread state (which=20
should now be safe!), if the other thread was in the middle of a=20
MONITORENTER.  Maybe there's a bug in Etienne's locking algorithm?

I don't have much experience with gdb, so I don't know if it can help=20
any more.  I don't think inserting breakpoints is going to do much,=20
since it fails randomly in a commonly called function.  I suppose it=20
would be useful to know why pthread_mutex_lock() causes a segfault --=20
but I can't even find pthread.c on the school machines.

http://www.opengroup.org/onlinepubs/007904975/functions/pthread_mutex_loc=
k.html

At the same time, I don't know what could be wrong with the locking=20
code, so ... I still need more pointers, if you've got them.  gdb output =

follows, if it's any help . . .

Can you (or somebody else) confirm the failure?

Cheers, and thanks,
Chris

P.S.  Again, this is a problem on uniprocessors.

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=


#0  0x400bbe90 in pthread_mutex_lock () from /lib/libpthread.so.0
#1  0x4009a0a2 in _svmf_enter_object_monitor (env=3D0x8068e50,=20
instance=3D0x402a6014)
     at thread.c:863
#2  0x4007035d in _svmf_interpreter (_env=3D0x8068e50) at=20
instructions_switch.c:15949
#3  0x40028c50 in _svmh_invoke_static_virtualmachine_runthread=20
(env=3D0x8068e50)
     at method_invoke.c:5065
#4  0x4001f208 in _svmf_thread_start (_env=3D0x8068e50) at thread.c:1195
#5  0x400bb0ba in pthread_start_thread () from /lib/libpthread.so.0
#6  0x401dcd6a in clone () from /lib/libc.so.6
(gdb) info f
Stack level 0, frame at 0xbf3ff59c:
  eip =3D 0x400bbe90 in pthread_mutex_lock; saved eip 0x4009a0a2
  called by frame at 0xbf3ff5ec
  Arglist at 0xbf3ff594, args:
  Locals at 0xbf3ff594, Previous frame's sp is 0xbf3ff59c
  Saved registers:
   ebx at 0xbf3ff57c, ebp at 0xbf3ff594, esi at 0xbf3ff580, edi at=20
0xbf3ff584,
   eip at 0xbf3ff598
(gdb) up
#1  0x4009a0a2 in _svmf_enter_object_monitor (env=3D0x8068e50,=20
instance=3D0x402a6014)
     at thread.c:863
863               _svmm_mutex_lock (owner->contention.owner.mutex);
(gdb) info f
Stack level 1, frame at 0xbf3ff5ec:
  eip =3D 0x4009a0a2 in _svmf_enter_object_monitor (thread.c:863);
     saved eip 0x4007035d
  called by frame at 0xbf3ffaac, caller of frame at 0xbf3ff59c
  source language c.
  Arglist at 0xbf3ff5e4, args: env=3D0x8068e50, instance=3D0x402a6014
  Locals at 0xbf3ff5e4, Previous frame's sp is 0xbf3ff5ec
  Saved registers:
   ebx at 0xbf3ff5ac, ebp at 0xbf3ff5e4, esi at 0xbf3ff5b0, edi at=20
0xbf3ff5b4,
   eip at 0xbf3ff5e8
(gdb) up
#2  0x4007035d in _svmf_interpreter (_env=3D0x8068e50) at=20
instructions_switch.c:15949
15949                 if (_svmf_enter_object_monitor (env, instance) !=3D=
=20
JNI_OK)
(gdb) info f
Stack level 2, frame at 0xbf3ffaac:
  eip =3D 0x4007035d in _svmf_interpreter (instructions_switch.c:15949);
     saved eip 0x40028c50
  called by frame at 0xbf3ffafc, caller of frame at 0xbf3ff5ec
  source language c.
  Arglist at 0xbf3ffaa4, args: _env=3D0x8068e50
  Locals at 0xbf3ffaa4, Previous frame's sp is 0xbf3ffaac
  Saved registers:
   ebx at 0xbf3ff5fc, ebp at 0xbf3ffaa4, esi at 0xbf3ff600, edi at=20
0xbf3ff604,
   eip at 0xbf3ffaa8
(gdb) info args
_env =3D (_svmt_JNIEnv *) 0x8068e50
(gdb) do
#1  0x4009a0a2 in _svmf_enter_object_monitor (env=3D0x8068e50,=20
instance=3D0x402a6014)
     at thread.c:863
863               _svmm_mutex_lock (owner->contention.owner.mutex);
(gdb) info args
env =3D (_svmt_JNIEnv *) 0x8068e50
instance =3D (_svmt_object_instance *) 0x402a6014
(gdb) info locals
_svmx_pmutex =3D (pthread_mutex_t *) 0x44
owner_id =3D 0
owner =3D (_svmt_JNIEnv *) 0x0
old_flag =3D 1094100508
notified =3D 0 '\0'
env =3D (_svmt_JNIEnv *) 0x8068e50
instance =3D (_svmt_object_instance *) 0x402a6014
vm =3D (_svmt_JavaVM *) 0x804cd48
old_lockword =3D 17
(gdb) do
#0  0x400bbe90 in pthread_mutex_lock () from /lib/libpthread.so.0
(gdb) info locals
No symbol table info available.
(gdb) q