From 666f164f4fbfa78bd00fb4b74788b42a39842c64 Mon Sep 17 00:00:00 2001
From: Roland McGrath <roland@redhat.com>
Date: Tue, 8 Apr 2008 23:12:30 -0700
Subject: [PATCH] fix dangling zombie when new parent ignores children
This fixes an arcane bug that we think was a regression introduced
by commit b2b2cbc4b2a2f389442549399a993a8306420baf. When a parent
ignores SIGCHLD (or uses SA_NOCLDWAIT), its children would self-reap
but they don't if it's using ptrace on them. When the parent thread
later exits and ceases to ptrace a child but leaves other live
threads in the parent's thread group, any zombie children are left
dangling. The fix makes them self-reap then, as they would have
done earlier if ptrace had not been in use.
Signed-off-by: Roland McGrath <roland@redhat.com>
---
kernel/exit.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/kernel/exit.c b/kernel/exit.c
index a2af6cac823c..93d2711b9381 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -702,6 +702,23 @@ static void exit_mm(struct task_struct * tsk)
mmput(mm);
}
+/*
+ * Return nonzero if @parent's children should reap themselves.
+ *
+ * Called with write_lock_irq(&tasklist_lock) held.
+ */
+static int ignoring_children(struct task_struct *parent)
+{
+ 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;
+}
+
/*
* Detach all tasks we were using ptrace on.
* Any that need to be release_task'd are put on the @dead list.
@@ -711,6 +728,7 @@ static void exit_mm(struct task_struct * tsk)
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);
@@ -726,10 +744,18 @@ static void ptrace_exit(struct task_struct *parent, struct list_head *dead)
* release_task() here because we already hold tasklist_lock.
*
* If it's our own child, there is no notification to do.
+ * But if our normal children self-reap, then this child
+ * was prevented by ptrace and we must reap it now.
*/
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;
+ }
}
if (task_detached(p)) {
--
2.20.1