• Oleg Nesterov's avatar
    do_wait: fix waiting for the group stop with the dead leader · 90bc8d8b
    Oleg Nesterov authored
    do_wait(WSTOPPED) assumes that p->state must be == TASK_STOPPED, this is
    not true if the leader is already dead.  Check SIGNAL_STOP_STOPPED instead
    and use signal->group_exit_code.
    
    Trivial test-case:
    
    	void *tfunc(void *arg)
    	{
    		pause();
    		return NULL;
    	}
    
    	int main(void)
    	{
    		pthread_t thr;
    		pthread_create(&thr, NULL, tfunc, NULL);
    		pthread_exit(NULL);
    		return 0;
    	}
    
    It doesn't react to ^Z (and then to ^C or ^\). The task is stopped, but
    bash can't see this.
    
    The bug is very old, and it was reported multiple times. This patch was sent
    more than a year ago (http://marc.info/?t=119713920000003) but it was ignored.
    
    This change also fixes other oddities (but not all) in this area.  For
    example, before this patch:
    
    	$ sleep 100
    	^Z
    	[1]+  Stopped                 sleep 100
    	$ strace -p `pidof sleep`
    	Process 11442 attached - interrupt to quit
    
    strace hangs in do_wait(), because ->exit_code was already consumed by
    bash.  After this patch, strace happily proceeds:
    
    	--- SIGTSTP (Stopped) @ 0 (0) ---
    	restart_syscall(<... resuming interrupted call ...>
    
    To me, this looks much more "natural" and correct.
    
    Another example.  Let's suppose we have the main thread M and sub-thread
    T, the process is stopped, and its parent did wait(WSTOPPED).  Now we can
    ptrace T but not M.  This looks at least strange to me.
    
    Imho, do_wait() should not confuse the per-thread ptrace stops with the
    per-process job control stops.
    Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: "Eric W. Biederman" <ebiederm@xmission.com>
    Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
    Cc: Kaz Kylheku <kkylheku@gmail.com>
    Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
    Cc: Roland McGrath <roland@redhat.com>
    Cc: Ulrich Drepper <drepper@redhat.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    90bc8d8b
exit.c 45.8 KB