From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Brauner Subject: Re: [PATCH v4] signal: add taskfd_send_signal() syscall Date: Thu, 6 Dec 2018 13:53:57 +0100 Message-ID: <20181206125354.ef3zlg3o75w32ymx@brauner.io> References: <20181206121858.12215-1-christian@brauner.io> <87h8fq7s84.fsf@oldenburg2.str.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: <87h8fq7s84.fsf@oldenburg2.str.redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Florian Weimer Cc: linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, luto@kernel.org, arnd@arndb.de, ebiederm@xmission.com, serge@hallyn.com, jannh@google.com, akpm@linux-foundation.org, oleg@redhat.com, cyphar@cyphar.com, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, dancol@google.com, timmurray@google.com, linux-man@vger.kernel.org, keescook@chromium.org, tglx@linutronix.de, x86@kernel.org List-Id: linux-api@vger.kernel.org On Thu, Dec 06, 2018 at 01:30:19PM +0100, Florian Weimer wrote: > * Christian Brauner: > > > /* zombies */ > > Zombies can be signaled just as any other process. No special error will be > > reported since a zombie state is an unreliable state (cf. [3]). > > I still disagree with this analysis. If I know that the target process > is still alive, and it is not, this is a persistent error condition > which can be reliably reported. Given that someone might send SIGKILL > to the process behind my back, detecting this error condition could be > useful. Apart from my objection that this is not actually a reliable state because of timing issues between e.g. calling wait and a process exiting I have two more concerns and one helpful suggestion. First, this is hooking pretty deep into kernel internals. So far EXIT_ZOMBIE is only exposed in kernel/exit.c and I don't see enough value to drag all of this into kernel/signal.c Second, all other signal syscalls don't do report errors when signaling to zombies as well. It would be odd if this one suddenly did. Third, if this really becomes such a big issue for userspace in the future that we want to do that work then we can add a flag like TASKFD_DETECT_ZOMBIE (or some such name) that will allow userspace to get an error back when signaling a zombie. As far as I'm concerned, this is out of scope for an initial implementation. We are going to use fds for tasks that's enough excitement for one patchset! > > Rest looks good to me (with the usual caveats). I take it that's your way of saying Acked-by? :) Christian