• Tejun Heo's avatar
    ptrace: implement PTRACE_LISTEN · 544b2c91
    Tejun Heo authored
    The previous patch implemented async notification for ptrace but it
    only worked while trace is running.  This patch introduces
    PTRACE_LISTEN which is suggested by Oleg Nestrov.
    
    It's allowed iff tracee is in STOP trap and puts tracee into
    quasi-running state - tracee never really runs but wait(2) and
    ptrace(2) consider it to be running.  While ptracer is listening,
    tracee is allowed to re-enter STOP to notify an async event.
    Listening state is cleared on the first notification.  Ptracer can
    also clear it by issuing INTERRUPT - tracee will re-trap into STOP
    with listening state cleared.
    
    This allows ptracer to monitor group stop state without running tracee
    - use INTERRUPT to put tracee into STOP trap, issue LISTEN and then
    wait(2) to wait for the next group stop event.  When it happens,
    PTRACE_GETSIGINFO provides information to determine the current state.
    
    Test program follows.
    
      #define PTRACE_SEIZE		0x4206
      #define PTRACE_INTERRUPT	0x4207
      #define PTRACE_LISTEN		0x4208
    
      #define PTRACE_SEIZE_DEVEL	0x80000000
    
      static const struct timespec ts1s = { .tv_sec = 1 };
    
      int main(int argc, char **argv)
      {
    	  pid_t tracee, tracer;
    	  int i;
    
    	  tracee = fork();
    	  if (!tracee)
    		  while (1)
    			  pause();
    
    	  tracer = fork();
    	  if (!tracer) {
    		  siginfo_t si;
    
    		  ptrace(PTRACE_SEIZE, tracee, NULL,
    			 (void *)(unsigned long)PTRACE_SEIZE_DEVEL);
    		  ptrace(PTRACE_INTERRUPT, tracee, NULL, NULL);
    	  repeat:
    		  waitid(P_PID, tracee, NULL, WSTOPPED);
    
    		  ptrace(PTRACE_GETSIGINFO, tracee, NULL, &si);
    		  if (!si.si_code) {
    			  printf("tracer: SIG %d\n", si.si_signo);
    			  ptrace(PTRACE_CONT, tracee, NULL,
    				 (void *)(unsigned long)si.si_signo);
    			  goto repeat;
    		  }
    		  printf("tracer: stopped=%d signo=%d\n",
    			 si.si_signo != SIGTRAP, si.si_signo);
    		  if (si.si_signo != SIGTRAP)
    			  ptrace(PTRACE_LISTEN, tracee, NULL, NULL);
    		  else
    			  ptrace(PTRACE_CONT, tracee, NULL, NULL);
    		  goto repeat;
    	  }
    
    	  for (i = 0; i < 3; i++) {
    		  nanosleep(&ts1s, NULL);
    		  printf("mother: SIGSTOP\n");
    		  kill(tracee, SIGSTOP);
    		  nanosleep(&ts1s, NULL);
    		  printf("mother: SIGCONT\n");
    		  kill(tracee, SIGCONT);
    	  }
    	  nanosleep(&ts1s, NULL);
    
    	  kill(tracer, SIGKILL);
    	  kill(tracee, SIGKILL);
    	  return 0;
      }
    
    This is identical to the program to test TRAP_NOTIFY except that
    tracee is PTRACE_LISTEN'd instead of PTRACE_CONT'd when group stopped.
    This allows ptracer to monitor when group stop ends without running
    tracee.
    
      # ./test-listen
      tracer: stopped=0 signo=5
      mother: SIGSTOP
      tracer: SIG 19
      tracer: stopped=1 signo=19
      mother: SIGCONT
      tracer: stopped=0 signo=5
      tracer: SIG 18
      mother: SIGSTOP
      tracer: SIG 19
      tracer: stopped=1 signo=19
      mother: SIGCONT
      tracer: stopped=0 signo=5
      tracer: SIG 18
      mother: SIGSTOP
      tracer: SIG 19
      tracer: stopped=1 signo=19
      mother: SIGCONT
      tracer: stopped=0 signo=5
      tracer: SIG 18
    
    -v2: Moved JOBCTL_LISTENING check in wait_task_stopped() into
         task_stopped_code() as suggested by Oleg.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Cc: Oleg Nesterov <oleg@redhat.com>
    544b2c91
sched.h 79.4 KB