Messages in this thread Patch in this message | | | Date | Thu, 29 Jan 2009 05:29:17 +0100 | From | Oleg Nesterov <> | Subject | [PATCH 2/4] ptrace: simplify ptrace_exit()->ignoring_children() path |
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ignoring_children() takes parent->sighand->siglock and checks k_sigaction[SIGCHLD] atomically. But this buys nothing, we can't get the "really" wrong result even if we race with sigaction(SIGCHLD). If we read the "stale" sa_handler/sa_flags we can pretend it was changed right after the check.
Remove spin_lock(->siglock), and kill "int ign" which caches the result of ignoring_children() which becomes rather trivial.
Perhaps it makes sense to export this helper, do_notify_parent() can use it too.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
--- 6.29-rc3/kernel/exit.c~2_IGN_SIGCHLD 2009-01-19 10:44:33.000000000 +0100 +++ 6.29-rc3/kernel/exit.c 2009-01-29 02:46:42.000000000 +0100 @@ -729,20 +729,12 @@ static void exit_mm(struct task_struct * } /* - * Return nonzero if @parent's children should reap themselves. - * - * Called with write_lock_irq(&tasklist_lock) held. + * Return nonzero if childs should reap themselves. */ -static int ignoring_children(struct task_struct *parent) +static int ignoring_children(struct sighand_struct *sigh) { - int ret; - struct sighand_struct *psig = parent->sighand; - unsigned long flags; - spin_lock_irqsave(&psig->siglock, flags); - ret = (psig->action[SIGCHLD-1].sa.sa_handler == SIG_IGN || - (psig->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT)); - spin_unlock_irqrestore(&psig->siglock, flags); - return ret; + return sigh->action[SIGCHLD-1].sa.sa_handler == SIG_IGN || + sigh->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT; } /* @@ -754,7 +746,6 @@ static int ignoring_children(struct task static void ptrace_exit(struct task_struct *parent, struct list_head *dead) { struct task_struct *p, *n; - int ign = -1; list_for_each_entry_safe(p, n, &parent->ptraced, ptrace_entry) { __ptrace_unlink(p); @@ -776,12 +767,8 @@ static void ptrace_exit(struct task_stru if (!task_detached(p) && thread_group_empty(p)) { if (!same_thread_group(p->real_parent, parent)) do_notify_parent(p, p->exit_signal); - else { - if (ign < 0) - ign = ignoring_children(parent); - if (ign) - p->exit_signal = -1; - } + else if (ignoring_children(parent->sighand)) + p->exit_signal = -1; } if (task_detached(p)) {
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