Commit 6d69cb87 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

ptrace: simplify ptrace_exit()->ignoring_children() path 



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: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 95c3eb76

kernel/exit.c

+8 −17
Original line number Diff line number Diff line
@@ -732,19 +732,15 @@ static void exit_mm(struct task_struct * tsk) 
}



/*

 * Return nonzero if @parent's children should reap themselves.

 *

 * Called with write_lock_irq(&tasklist_lock) held.

 * Called with irqs disabled, returns true 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);

	spin_lock(&sigh->siglock);

	ret = (sigh->action[SIGCHLD-1].sa.sa_handler == SIG_IGN) ||

	      (sigh->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT);

	spin_unlock(&sigh->siglock);

	return ret;

}
@@ -757,7 +753,6 @@ static int ignoring_children(struct task_struct *parent) 
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);
@@ -779,13 +774,9 @@ static void ptrace_exit(struct task_struct *parent, struct list_head *dead) 
		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)

			else if (ignoring_children(parent->sighand))

				p->exit_signal = -1;

		}

		}



		if (task_detached(p)) {

			/*

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