do_wait: fix waiting for the group stop with the dead leader
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: Oleg 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: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -1417,6 +1417,18 @@ static int wait_task_zombie(struct task_struct *p, int options,
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return retval;
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}
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static int *task_stopped_code(struct task_struct *p, bool ptrace)
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{
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if (ptrace) {
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if (task_is_stopped_or_traced(p))
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return &p->exit_code;
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} else {
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if (p->signal->flags & SIGNAL_STOP_STOPPED)
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return &p->signal->group_exit_code;
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}
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return NULL;
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}
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/*
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* Handle sys_wait4 work for one task in state TASK_STOPPED. We hold
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* read_lock(&tasklist_lock) on entry. If we return zero, we still hold
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@ -1427,7 +1439,7 @@ static int wait_task_stopped(int ptrace, struct task_struct *p,
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int options, struct siginfo __user *infop,
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int __user *stat_addr, struct rusage __user *ru)
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{
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int retval, exit_code, why;
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int retval, exit_code, *p_code, why;
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uid_t uid = 0; /* unneeded, required by compiler */
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pid_t pid;
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@ -1437,22 +1449,16 @@ static int wait_task_stopped(int ptrace, struct task_struct *p,
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exit_code = 0;
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spin_lock_irq(&p->sighand->siglock);
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if (unlikely(!task_is_stopped_or_traced(p)))
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p_code = task_stopped_code(p, ptrace);
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if (unlikely(!p_code))
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goto unlock_sig;
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if (!ptrace && p->signal->group_stop_count > 0)
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/*
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* A group stop is in progress and this is the group leader.
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* We won't report until all threads have stopped.
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*/
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goto unlock_sig;
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exit_code = p->exit_code;
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exit_code = *p_code;
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if (!exit_code)
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goto unlock_sig;
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if (!unlikely(options & WNOWAIT))
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p->exit_code = 0;
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*p_code = 0;
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/* don't need the RCU readlock here as we're holding a spinlock */
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uid = __task_cred(p)->uid;
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@ -1608,7 +1614,7 @@ static int wait_consider_task(struct task_struct *parent, int ptrace,
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*/
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*notask_error = 0;
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if (task_is_stopped_or_traced(p))
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if (task_stopped_code(p, ptrace))
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return wait_task_stopped(ptrace, p, options,
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infop, stat_addr, ru);
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