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Commit c7122344 authored by Andrei Vagin's avatar Andrei Vagin Committed by Greg Kroah-Hartman
Browse files

kernel/exit.c: release ptraced tasks before zap_pid_ns_processes 

commit 8fb335e078378c8426fabeed1ebee1fbf915690c upstream.

Currently, exit_ptrace() adds all ptraced tasks in a dead list, then
zap_pid_ns_processes() waits on all tasks in a current pidns, and only
then are tasks from the dead list released.

zap_pid_ns_processes() can get stuck on waiting tasks from the dead
list.  In this case, we will have one unkillable process with one or
more dead children.

Thanks to Oleg for the advice to release tasks in find_child_reaper().

Link: http://lkml.kernel.org/r/20190110175200.12442-1-avagin@gmail.com


Fixes: 7c8bd232 ("exit: ptrace: shift "reap dead" code from exit_ptrace() to forget_original_parent()")
Signed-off-by: default avatarAndrei Vagin <avagin@gmail.com>
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 9ee5987f

kernel/exit.c

+10 −2
Original line number Diff line number Diff line
@@ -558,12 +558,14 @@ static struct task_struct *find_alive_thread(struct task_struct *p) 
	return NULL;

}



static struct task_struct *find_child_reaper(struct task_struct *father)

static struct task_struct *find_child_reaper(struct task_struct *father,

						struct list_head *dead)

	__releases(&tasklist_lock)

	__acquires(&tasklist_lock)

{

	struct pid_namespace *pid_ns = task_active_pid_ns(father);

	struct task_struct *reaper = pid_ns->child_reaper;

	struct task_struct *p, *n;



	if (likely(reaper != father))

		return reaper;
@@ -579,6 +581,12 @@ static struct task_struct *find_child_reaper(struct task_struct *father) 
		panic("Attempted to kill init! exitcode=0x%08x\n",

			father->signal->group_exit_code ?: father->exit_code);

	}



	list_for_each_entry_safe(p, n, dead, ptrace_entry) {

		list_del_init(&p->ptrace_entry);

		release_task(p);

	}



	zap_pid_ns_processes(pid_ns);

	write_lock_irq(&tasklist_lock);
@@ -668,7 +676,7 @@ static void forget_original_parent(struct task_struct *father, 
		exit_ptrace(father, dead);



	/* Can drop and reacquire tasklist_lock */

	reaper = find_child_reaper(father);

	reaper = find_child_reaper(father, dead);

	if (list_empty(&father->children))

		return;