From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io1-f66.google.com ([209.85.166.66]:39700 "EHLO mail-io1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729455AbfAHSZ6 (ORCPT ); Tue, 8 Jan 2019 13:25:58 -0500 Received: by mail-io1-f66.google.com with SMTP id k7so3904607iob.6 for ; Tue, 08 Jan 2019 10:25:57 -0800 (PST) Date: Tue, 8 Jan 2019 11:25:54 -0700 From: Tycho Andersen To: Christian Brauner Cc: "Serge E. Hallyn" , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, luto@kernel.org, arnd@arndb.de, keescook@chromium.org, akpm@linux-foundation.org, jannh@google.com, oleg@redhat.com, cyphar@cyphar.com, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, dancol@google.com, timmurray@google.com, fweimer@redhat.com, tglx@linutronix.de, x86@kernel.org, ebiederm@xmission.com Subject: Re: [PATCH v7 2/2] selftests: add tests for pidfd_send_signal() Message-ID: <20190108182554.GB28330@cisco> References: <20190102161654.9093-1-christian@brauner.io> <20190102161654.9093-2-christian@brauner.io> <20190108175306.GF29009@cisco> <20190108175415.GA22353@mail.hallyn.com> <20190108175843.GA26016@cisco> <20190108181742.GA22614@mail.hallyn.com> <20190108182023.GA28330@cisco> <20190108182444.e6kq2gqftde23jou@brauner.io> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190108182444.e6kq2gqftde23jou@brauner.io> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue, Jan 08, 2019 at 07:24:46PM +0100, Christian Brauner wrote: > On Tue, Jan 08, 2019 at 11:20:23AM -0700, Tycho Andersen wrote: > > On Tue, Jan 08, 2019 at 12:17:42PM -0600, Serge E. Hallyn wrote: > > > On Tue, Jan 08, 2019 at 10:58:43AM -0700, Tycho Andersen wrote: > > > > On Tue, Jan 08, 2019 at 11:54:15AM -0600, Serge E. Hallyn wrote: > > > > > On Tue, Jan 08, 2019 at 10:53:06AM -0700, Tycho Andersen wrote: > > > > > > On Wed, Jan 02, 2019 at 05:16:54PM +0100, Christian Brauner wrote: > > > > > > > + /* > > > > > > > + * Stop the child so we can inspect whether we have > > > > > > > + * recycled pid PID_RECYCLE. > > > > > > > + */ > > > > > > > + close(pipe_fds[0]); > > > > > > > + ret = kill(recycled_pid, SIGSTOP); > > > > > > > + close(pipe_fds[1]); > > > > > > > + if (ret) { > > > > > > > + (void)wait_for_pid(recycled_pid); > > > > > > > + _exit(PIDFD_ERROR); > > > > > > > + } > > > > > > > > > > > > Sorry for being late to the party, but I wonder if this whole thing > > > > > > couldn't be simplified with /proc/sys/kenrel/ns_last_pid? > > > > > > > > > > no, bc it's not namespaced :) > > > > > > > > Huh? It looks like it is... > > > > > > > > static int pid_ns_ctl_handler(struct ctl_table *table, int write, > > > > void __user *buffer, size_t *lenp, loff_t *ppos) > > > > { > > > > struct pid_namespace *pid_ns = task_active_pid_ns(current); > > > > struct ctl_table tmp = *table; > > > > int ret, next; > > > > > > > > if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN)) > > > > return -EPERM; > > > > > > > > ... > > > > > > Oh - hah, but that's ns_last_pid. You'd want pid_max. And that one > > > is not namespaced. > > > > Perhaps I'm misunderstanding, but isn't the point of all this code to > > get the same pid again? So can't we just fork(), kill(), then set > > ns_last_pid to pid-1, and fork() again to re-use? > > Maybe. It's just a selftest that works reliably as it is so unless > there's a technical issue with the patch I'm not going to do another > version just because of that unless people feel super strongly about > this. > Another advantage is that the code we have right now works even when > CONFIG_CHECKPOINT_RESTORE is not selected. No, it's fine as is. Just a lot less code if we do it the other way. Cheers, Tycho