Messages in this thread Patch in this message | | | Date | Tue, 8 Jan 2019 17:50:43 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH] kernel: release ptraced tasks before zap_pid_ns_processes |
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Sorry for delay, vacation,
On 01/02, Andrei Vagin wrote: > > zap_pid_ns_processes() can stuck on waiting tasks from the dead list. In > this case, we will have one unkillable process with one or more dead > children.
Thanks!
> --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -664,9 +664,6 @@ static void forget_original_parent(struct task_struct *father, > { > struct task_struct *p, *t, *reaper; > > - if (unlikely(!list_empty(&father->ptraced))) > - exit_ptrace(father, dead); > - > /* Can drop and reacquire tasklist_lock */ > reaper = find_child_reaper(father); > if (list_empty(&father->children)) > @@ -705,8 +702,18 @@ static void exit_notify(struct task_struct *tsk, int group_dead) > LIST_HEAD(dead); > > write_lock_irq(&tasklist_lock); > - forget_original_parent(tsk, &dead); > + if (unlikely(!list_empty(&tsk->ptraced))) > + exit_ptrace(tsk, &dead); > + write_unlock_irq(&tasklist_lock); > + > + /* Ptraced tasks have to be released before zap_pid_ns_processes(). */ > + list_for_each_entry_safe(p, n, &dead, ptrace_entry) { > + list_del_init(&p->ptrace_entry); > + release_task(p); > + } > > + write_lock_irq(&tasklist_lock); > + forget_original_parent(tsk, &dead); > if (group_dead) > kill_orphaned_pgrp(tsk->group_leader, NULL);
How about a different fix below? It avoids additional write_lock/unlock(tasklist), and another list_for_each_entry_safe(dead) loop is called only if it is actually needed.
Or I missed something?
Oleg.
--- x/kernel/exit.c +++ x/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 +581,11 @@ 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 +675,7 @@ 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;
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