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Biederman" Subject: Re: [PATCH] kernel: release ptraced tasks before zap_pid_ns_processes Message-ID: <20190108203612.GA19454@gmail.com> References: <20190102205939.26231-1-avagin@gmail.com> <20190108165043.GA10240@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=koi8-r Content-Disposition: inline In-Reply-To: <20190108165043.GA10240@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 08, 2019 at 05:50:43PM +0100, Oleg Nesterov wrote: > 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? No, you don't. The patch looks really nice. Thanks! BTW: We probably need to add the "Fixes:" tag, but I am not sure to which commit, it looks like the issue is here for years. Acked-by: Andrei Vagin > > 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; > >