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fix dangling zombie when new parent ignores children 

This fixes an arcane bug that we think was a regression introduced
by commit b2b2cbc4b2.  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>
This commit is contained in:
Roland McGrath 2008-04-08 23:12:30 -07:00
parent 14dd0b8141
commit 666f164f4f
1 changed files with 26 additions and 0 deletions
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26
kernel/exit.c
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@ -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)) {