From: Andrei Vagin Date: Fri, 1 Feb 2019 22:20:24 +0000 (-0800) Subject: kernel/exit.c: release ptraced tasks before zap_pid_ns_processes X-Git-Tag: v4.9.155~8 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=44ccc0cce1e1250a11474acda2870c39cafa2b67;p=platform%2Fkernel%2Flinux-amlogic.git 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: 7c8bd2322c7f ("exit: ptrace: shift "reap dead" code from exit_ptrace() to forget_original_parent()") Signed-off-by: Andrei Vagin Signed-off-by: Oleg Nesterov Cc: "Eric W. Biederman" Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/exit.c b/kernel/exit.c index 6dd7ff4..d9394fc 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -525,12 +525,14 @@ 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; @@ -546,6 +548,12 @@ 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); @@ -632,7 +640,7 @@ 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;