The patch titled
Subject: kernel/exit.c: release ptraced tasks before zap_pid_ns_processes
has been added to the -mm tree. Its filename is
kernel-release-ptraced-tasks-before-zap_pid_ns_processes.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/kernel-release-ptraced-tasks-before-zap_pid_ns_processes.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/kernel-release-ptraced-tasks-before-zap_pid_ns_processes.patch
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------------------------------------------------------
From: Andrei Vagin <avagin@xxxxxxxxx>
Subject: kernel/exit.c: release ptraced tasks before zap_pid_ns_processes
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@xxxxxxxxx
Fixes: 7c8bd2322c7f ("exit: ptrace: shift "reap dead" code from exit_ptrace() to forget_original_parent()")
Signed-off-by: Andrei Vagin <avagin@xxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/kernel/exit.c~kernel-release-ptraced-tasks-before-zap_pid_ns_processes
+++ a/kernel/exit.c
@@ -558,12 +558,14 @@ static struct task_struct *find_alive_th
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_re
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(struc
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;
_
Patches currently in -mm which might be from avagin@xxxxxxxxx are
kernel-release-ptraced-tasks-before-zap_pid_ns_processes.patch
ptrace-take-into-account-saved_sigmask-in-ptrace_getsetsigmask.patch
include-replace-tsk-to-task-in-linux-sched-signalh.patch
