pointless pthread background activity

[Zomb]

Hello,

this is a followup to ​https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=826990 , see there for details.

Yes, I can use strace and gdb, this gets me:

[pid 20242] [00007f7f47f38408] <... futex resumed> ) = -1 ETIMEDOUT (Connection timed out)
[pid 20242] [00007f7f47f3ad7a] futex(0x7f7f3000de60, FUTEX_WAKE_PRIVATE, 1) = 0
[pid 20242] [00007f7f47f38408] futex(0x7f7f3000de34, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 30849, {1466101302, 432613425}, ffffffff <unfinished ...>

or

[pid 20242] [00007f7f47f38408] futex(0x7f7f3000de34, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 30847, {1466101301, 433070291}, ffffffff <unfinished ...>
[pid 20283] [00007f7f47f38408] <... restart_syscall resumed> ) = -1 ETIMEDOUT (Connection timed out)
[pid 20283] [00007f7f47f3ad7a] futex(0x7f7f3005f0c0, FUTEX_WAKE_PRIVATE, 1) = 0
[pid 20283] [00007f7f47f38408] futex(0x7f7f3005f094, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 33041, {1466101301, 186292874}, ffffffff) = -1 ETIMEDOUT (Connection timed out)
[pid 20283] [00007f7f47f3ad7a] futex(0x7f7f3005f0c0, FUTEX_WAKE_PRIVATE, 1) = 0
[pid 20283] [00007f7f47f38408] futex(0x7f7f3005f094, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 33043, {1466101301, 686744289}, ffffffff <unfinished ...>

(gdb) break *0x00007f7f47f3ad7a
Breakpoint 1 at 0x7f7f47f3ad7a: file ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S, line 371.
(gdb) cont
Continuing.
[Switching to Thread 0x7f7f2dc92700 (LWP 20283)]

Breakpoint 1, __lll_unlock_wake () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:371
371	../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S: Datei oder Verzeichnis nicht gefunden.
(gdb) bt
#0  __lll_unlock_wake () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:371
#1  0x00007f7f47f36101 in __pthread_mutex_unlock_usercnt (mutex=mutex@entry=0x7f7f3005f0c0, decr=decr@entry=1) at pthread_mutex_unlock.c:57
#2  0x00007f7f47f361ca in __GI___pthread_mutex_unlock (mutex=mutex@entry=0x7f7f3005f0c0) at pthread_mutex_unlock.c:315
#3  0x00007f7f47c5b31a in rtSemEventWait (fAutoResume=true, cMillies=500, hEventSem=0x7f7f3005f090)
    at /var/tmp/virtualbox-5.0.20-dfsg/src/VBox/Runtime/r3/linux/../posix/semevent-posix.cpp:485
#4  RTSemEventWait (hEventSem=0x7f7f3005f090, cMillies=500) at /var/tmp/virtualbox-5.0.20-dfsg/src/VBox/Runtime/r3/linux/../posix/semevent-posix.cpp:496
#5  0x0000000000483e22 in VirtualBox::ClientWatcher::worker (pvUser=0x7f7f30047f20) at /var/tmp/virtualbox-5.0.20-dfsg/src/VBox/Main/src-server/ClientWatcher.cpp:731
#6  0x00007f7f47bdd25c in rtThreadMain (pThread=pThread@entry=0x7f7f30049000, NativeThread=NativeThread@entry=140184205731584, 
    pszThreadName=pszThreadName@entry=0x7f7f300498e0 "Watcher") at /var/tmp/virtualbox-5.0.20-dfsg/src/VBox/Runtime/common/misc/thread.cpp:717
#7  0x00007f7f47c5860c in rtThreadNativeMain (pvArgs=0x7f7f30049000) at /var/tmp/virtualbox-5.0.20-dfsg/src/VBox/Runtime/r3/posix/thread-posix.cpp:324
#8  0x00007f7f47f32464 in start_thread (arg=0x7f7f2dc92700) at pthread_create.c:334
#9  0x00007f7f46b5ae5d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
(gdb) break *0x7f7f3005f094
Breakpoint 2 at 0x7f7f3005f094
(gdb) cont
Continuing.
[Switching to Thread 0x7f7f3d899700 (LWP 20242)]

Breakpoint 1, __lll_unlock_wake () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:371
371	in ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S
(gdb) bt
#0  __lll_unlock_wake () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:371
#1  0x00007f7f47f36101 in __pthread_mutex_unlock_usercnt (mutex=mutex@entry=0x7f7f3000de60, decr=decr@entry=1) at pthread_mutex_unlock.c:57
#2  0x00007f7f47f361ca in __GI___pthread_mutex_unlock (mutex=mutex@entry=0x7f7f3000de60) at pthread_mutex_unlock.c:315
#3  0x00007f7f47c5b31a in rtSemEventWait (fAutoResume=true, cMillies=998, hEventSem=0x7f7f3000de30)
    at /var/tmp/virtualbox-5.0.20-dfsg/src/VBox/Runtime/r3/linux/../posix/semevent-posix.cpp:485
#4  RTSemEventWait (hEventSem=0x7f7f3000de30, cMillies=998) at /var/tmp/virtualbox-5.0.20-dfsg/src/VBox/Runtime/r3/linux/../posix/semevent-posix.cpp:496
#5  0x00007f7f47c2adc0 in rtTimerLRThread (hThreadSelf=<optimized out>, pvUser=0x7f7f3000c330) at /var/tmp/virtualbox-5.0.20-dfsg/src/VBox/Runtime/generic/timerlr-generic.cpp:341
#6  0x00007f7f47bdd25c in rtThreadMain (pThread=pThread@entry=0x7f7f3000a860, NativeThread=NativeThread@entry=140184470001408, 
    pszThreadName=pszThreadName@entry=0x7f7f3000b140 "TimerLR") at /var/tmp/virtualbox-5.0.20-dfsg/src/VBox/Runtime/common/misc/thread.cpp:717
#7  0x00007f7f47c5860c in rtThreadNativeMain (pvArgs=0x7f7f3000a860) at /var/tmp/virtualbox-5.0.20-dfsg/src/VBox/Runtime/r3/posix/thread-posix.cpp:324
#8  0x00007f7f47f32464 in start_thread (arg=0x7f7f3d899700) at pthread_create.c:334
#9  0x00007f7f46b5ae5d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
(gdb) cont
Continuing.
[Switching to Thread 0x7f7f4853e700 (LWP 20150)]

Breakpoint 1, __lll_unlock_wake () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:371
371	in ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S
(gdb) bt
#0  __lll_unlock_wake () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:371
#1  0x00007f7f47f36101 in __pthread_mutex_unlock_usercnt (mutex=mutex@entry=0x2ab3378, decr=decr@entry=1) at pthread_mutex_unlock.c:57
#2  0x00007f7f47f361ca in __GI___pthread_mutex_unlock (mutex=mutex@entry=0x2ab3378) at pthread_mutex_unlock.c:315
#3  0x00007f7f476931ec in VBoxNsprPR_Unlock (lock=lock@entry=0x2ab3378) at /var/tmp/virtualbox-5.0.20-dfsg/src/libs/xpcom18a4/nsprpub/pr/src/pthreads/ptsynch.c:220
#4  0x00007f7f476934bf in VBoxNsprPR_ExitMonitor (mon=0x2ab3370) at /var/tmp/virtualbox-5.0.20-dfsg/src/libs/xpcom18a4/nsprpub/pr/src/pthreads/ptsynch.c:546
#5  0x00007f7f47666e0e in nsAutoMonitor::Exit (this=this@entry=0x7f7f4853de30) at /var/tmp/virtualbox-5.0.20-dfsg/src/libs/xpcom18a4/xpcom/threads/nsAutoLock.cpp:405
#6  0x00007f7f3e09f3df in DConnectWorker::Run (this=0x2ab2860) at /var/tmp/virtualbox-5.0.20-dfsg/src/libs/xpcom18a4/ipc/ipcd/extensions/dconnect/src/ipcDConnectService.cpp:2970
#7  0x00007f7f476697f7 in nsThread::Main (arg=0x2ab2ad0) at /var/tmp/virtualbox-5.0.20-dfsg/src/libs/xpcom18a4/xpcom/threads/nsThread.cpp:118
#8  0x00007f7f47693f9f in _pt_root (arg=0x2ab3610) at /var/tmp/virtualbox-5.0.20-dfsg/src/libs/xpcom18a4/nsprpub/pr/src/pthreads/ptthread.c:224
#9  _pt_iprt_root (Thread=<optimized out>, pvUser=0x2ab3610) at /var/tmp/virtualbox-5.0.20-dfsg/src/libs/xpcom18a4/nsprpub/pr/src/pthreads/ptthread.c:272
#10 0x00007f7f47bdd25c in rtThreadMain (pThread=pThread@entry=0x2ab3780, NativeThread=NativeThread@entry=140184651032320, pszThreadName=pszThreadName@entry=0x2ab4060 "nspr-2")
    at /var/tmp/virtualbox-5.0.20-dfsg/src/VBox/Runtime/common/misc/thread.cpp:717
#11 0x00007f7f47c5860c in rtThreadNativeMain (pvArgs=0x2ab3780) at /var/tmp/virtualbox-5.0.20-dfsg/src/VBox/Runtime/r3/posix/thread-posix.cpp:324
#12 0x00007f7f47f32464 in start_thread (arg=0x7f7f4853e700) at pthread_create.c:334
#13 0x00007f7f46b5ae5d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Hope this helps.