Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752445AbbBWMn5 (ORCPT ); Mon, 23 Feb 2015 07:43:57 -0500 Received: from cantor2.suse.de ([195.135.220.15]:51086 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752181AbbBWMn4 (ORCPT ); Mon, 23 Feb 2015 07:43:56 -0500 Date: Mon, 23 Feb 2015 13:43:53 +0100 (CET) From: Jiri Kosina To: Ingo Molnar cc: Josh Poimboeuf , Vojtech Pavlik , Peter Zijlstra , Andrew Morton , Ingo Molnar , Seth Jennings , linux-kernel@vger.kernel.org, Linus Torvalds , live-patching@vger.kernel.org Subject: Re: live patching design (was: Re: [PATCH 1/3] sched: add sched_task_call()) In-Reply-To: <20150221183005.GB8406@gmail.com> Message-ID: References: <20150219214229.GD15980@treble.redhat.com> <20150220095003.GA23506@gmail.com> <20150220104418.GD25076@gmail.com> <20150220194901.GB3603@gmail.com> <20150220214613.GA21598@suse.com> <20150220220845.GI15980@treble.redhat.com> <20150221183005.GB8406@gmail.com> User-Agent: Alpine 2.00 (LNX 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1587 Lines: 36 On Sat, 21 Feb 2015, Ingo Molnar wrote: > (It does have some other requirements, such as making all > syscalls interruptible to a 'special' signalling method > that only live patching triggers - even syscalls that are > under the normal ABI uninterruptible, such as sys_sync().) BTW I didn't really understand this -- could you please elaborate what exactly do you propose to do here in your "simplified" patching method (i.e. serializing everybody at the kernel boundary) for TASK_UNINTERRUPTIBLE processess? That actually seems to be the most crucial problem to me in this respect. Other things are rather implementation details; no matter whether we are sending normal SIGCONT or SIGPATCHING with special semantics you have described above, at the end of the day we end up calling kick_process() for the task in question, and that makes both interruptible sleepers and CPU hogs go through the "checkpoint". SIGPATCHING would then be "just" an improvement of this, making sure that EINTR doesn't spuriously get leaked to userspace. But I didn't understand your claims regarding uninterruptible sleeps in your paragraph above. sys_sync() is one thing, that's just waiting uninterruptibly for completion. But how about all the mutex waitiers in TASK_UNINTERRUPTIBLE, for example? Thanks a lot, -- Jiri Kosina SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/