Re: Invisible threads in 2.6.9

[Patryk Jakubowski]

Michal Schmidt wrote:

> It doesn't work for me:
>
> # ps aux | grep [t]hread
> michich   7447  0.0  0.0     0    0 pts/1    Zl+  09:43   0:00 
> [threadbug] <defunct>
> # ps auwxH | grep [t]hread
> #
>
> And I can't inspect /proc directly:
>
> Isn't it strange?
>
> Michal Schmidt

Yes. It is badly strange for me. It is not the bug in procps. procps 
scans the /proc tree for information, top and ps too. I know that I'm 
amateur programmer, but not kernel programmer.

When i run this example program (threadbug) and let its PID be 6024. Its 
first subthread can be PID 6025 (for example). The lider thread exits. 
And /proc/6024/task is inaccesible, ls shows it empty. 
/proc/6024/task/6025 should exist. However, cat /proc/6025/cmdline 
returns ./threadbug. But ls -d /proc/602? do not shows /proc/6025. Any 
way. I'm almost sure that /proc/6024/task/* should be visible. It is bug 
in procfs filesystem or buggy strategy to show tasks in /proc.



I put here my session with threadbug. Important lines are prefixed with "!".

 pat@pat:/tmp$ cat > threadbug.c
 #include <pthread.h>
 #include <unistd.h>

 void *run(void *arg)
 {
     for(;;);
 }

 int main()
 {
     pthread_t t;
     int i;
     for (i = 0; i < 10; ++i)
         pthread_create(&t, NULL, run, NULL);
     sleep(30);
     pthread_exit(NULL);
 }

 pat@pat:/tmp$ gcc -o threadbug -lpthread threadbug.c

 pat@pat:/tmp$ ./threadbug &
 [1] 6907

 pat@pat:/tmp$ date
 Wed Oct  6 11:37:41 CEST 2004

! pat@pat:/tmp$ ls /proc/6907/task    # threads are detectable
 6907  6908  6909  6910  6911  6912  6913  6914  6915  6916  6917

 pat@pat:/tmp$ ps m
   PID TTY      STAT   TIME COMMAND
  1647 pts/0    -      0:00 /bin/bash
     - -        Ss     0:00 -
  6019 pts/2    -      0:00 /bin/bash
     - -        Ss     0:00 -
  6035 pts/3    -      0:00 /bin/bash
     - -        Ss+    0:00 -
  6907 pts/2    -      0:00 ./threadbug
     - -        S      0:00 -
     - -        R      0:06 -
     - -        R      0:06 -
     - -        R      0:06 -
     - -        R      0:05 -
     - -        R      0:06 -
     - -        R      0:06 -
     - -        R      0:06 -
     - -        R      0:05 -
     - -        R      0:07 -
     - -        R      0:07 -
  6928 pts/2    -      0:00 ps m
     - -        R+     0:00 -

! pat@pat:/tmp$ date    # now leader thread is exited
!  Wed Oct  6 11:40:15 CEST 2004

 pat@pat:/tmp$ ls /proc/6907/task
!  ls: /proc/6907/task: No such file or directory    # no threads and 
other info

 pat@pat:/tmp$ ps m
   PID TTY      STAT   TIME COMMAND
  1647 pts/0    -      0:00 /bin/bash
     - -        Ss     0:00 -
  6019 pts/2    -      0:00 /bin/bash
     - -        Ss     0:00 -
  6035 pts/3    -      0:00 /bin/bash
     - -        Ss+    0:00 -
  6907 pts/2    -      0:00 [threadbug] <defunct>
  6942 pts/2    -      0:00 ps m
     - -        R+     0:00 -

!  pat@pat:/tmp$ cat /proc/69[01]?/cmdline   # where are the threads?

!  pat@pat:/tmp$ cat /proc/6907/cmdline    # where is info?

 pat@pat:/tmp$ cat /proc/6908/cmdline    # some info is hidden here
 ./threadbug

 pat@pat:/tmp$ cat /proc/6909/cmdline
 ./threadbug

 pat@pat:/tmp$ cat /proc/6910/cmdline
./threadbug

! pat@pat:/tmp$ cat /proc/6910/status    # and here
 Name:   threadbug
 State:  R (running)
 SleepAVG:       0%
! Tgid:   6907
! Pid:    6910   # this is PID of the thread of process 6907
 PPid:   6019
 TracerPid:      0
 Uid:    1000    1000    1000    1000
 Gid:    100     100     100     100
 FDSize: 256
 Groups: 4 5 24 29 33 44 100 1001
 VmSize:    83528 kB
 VmLck:         0 kB
 VmRSS:       456 kB
 VmData:    82076 kB
 VmStk:        12 kB
 VmExe:         1 kB
 VmLib:     83343 kB
!  Threads:        11    # 10 subthreads and 1 leader thread
 SigPnd: 0000000000000000
 ShdPnd: 0000000000000000
 SigBlk: 0000000000000000
 SigIgn: 0000000000000000
 SigCgt: 0000000080000000
 CapInh: 0000000000000000
 CapPrm: 0000000000000000
 CapEff: 0000000000000000
 pat@pat:/tmp$ kill %1
 pat@pat:/tmp$
 [1]+  Terminated              ./threadbug
 pat@pat:/tmp$


I have checked threadbug program ont RedHat Enterprise with 2.4.21 
kernel with NPTL 0.60. Threads was visible after leader thread exits and 
process become zombie state.

My configuration:
Kernel: 2.6.9-rc9, SMP/SMT, not preemptible
libc6-2.3.2

GNU_LIBPTHREAD_VERSION = NPTL 0.60
P4 Presscott processor, HT
gcc-3.4




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