Return-Path: Received: from cantor2.suse.de ([195.135.220.15]:53351 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752483AbbFIMP2 (ORCPT ); Tue, 9 Jun 2015 08:15:28 -0400 Date: Tue, 9 Jun 2015 14:15:24 +0200 (CEST) From: Jiri Kosina To: Tejun Heo cc: Petr Mladek , Andrew Morton , Oleg Nesterov , Ingo Molnar , Peter Zijlstra , Richard Weinberger , Steven Rostedt , David Woodhouse , linux-mtd@lists.infradead.org, Trond Myklebust , Anna Schumaker , linux-nfs@vger.kernel.org, Chris Mason , "Paul E. McKenney" , Thomas Gleixner , Linus Torvalds , Borislav Petkov , Michal Hocko , live-patching@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 06/18] signal/kthread: Initial implementation of kthread signal handling In-Reply-To: <20150609071022.GX21465@mtj.duckdns.org> Message-ID: References: <1433516477-5153-1-git-send-email-pmladek@suse.cz> <1433516477-5153-7-git-send-email-pmladek@suse.cz> <20150609071022.GX21465@mtj.duckdns.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, 9 Jun 2015, Tejun Heo wrote: > While I agree that it'd be great to consolidate the existing kthread > signal users, I feel quite uncomfortable with doing full-fledged > signal handling for kthreads which try to mimic the userland behavior. > Most of the default behaviors don't make sense for kthreads and it'd > be awful to have different kthreads interpreting arbitrary signals for > differing custom behaviors, which often happens when there's no > default. I don't think the ultimate goal is to mimic what userspace does; especially when it comes to default actions. To me, the ultimate goal (*) is to make it possible for kthread to be able to decide whether it wants "some kind of default behavior" (however that'd be defined), or "ignore all", or "just handle this set of signals with these handlers", and make API for this that would avoid every kthread implementing its own complete signal handling. (*) Well, the ultimate goal really is to bring sanity to how kthreads are handling their main loop. Trying to bring some consistency to how kthreads are handling signals is just an (optional) added value on top of that. > While we do have several kthread signal users, they aren't too many and > majority of them use it to allow userland to tell it to shutdown and Yeah. Via SIGKILL. Or SIGTERM. Or SIGINT. Or SIGQUIT. Not really consistent either. > there seem to be a couple which use HUP/USR1 to cancel whatever it's > processing / waiting on at the moment. Hmmm... jffs uses STOP/CONT too. > I don't know how this should be done but let's please try to > > 1. Encourage uniform behaviors across the signals. Fully agreed. > 2. Ultimately discourage usage of signals on kthreads as this closely > ties implementation detail (use of single kthread) to the userland > visible interface in a way where we can't easily get back out of. > For example, what if jffs needs its gc workers to be multi-threaded > and per-NUMA for high-iops devices later on? What kind of multi-threading kthreads are you referring to here? Something more sophisticated than simply spawning several per-CPU (or per-whatever-resource) full-fledged kthreads? -- Jiri Kosina SUSE Labs