Date: Fri, 20 Feb 2015 16:08:45 -0600
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Vojtech Pavlik <vojtech@suse.com>
Cc: Ingo Molnar <mingo@kernel.org>, Jiri Kosina <jkosina@suse.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@redhat.com>, Seth Jennings <sjenning@redhat.com>,
        linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: live patching design (was: Re: [PATCH 1/3] sched: add
 sched_task_call())
Message-ID: <20150220220845.GI15980@treble.redhat.com>
References: <20150219204036.GA16882@suse.com>
 <20150219214229.GD15980@treble.redhat.com>
 <alpine.LNX.2.00.1502200830430.28769@pobox.suse.cz>
 <alpine.LNX.2.00.1502200939230.28769@pobox.suse.cz>
 <20150220095003.GA23506@gmail.com>
 <alpine.LNX.2.00.1502201052050.28769@pobox.suse.cz>
 <20150220104418.GD25076@gmail.com>
 <alpine.LNX.2.00.1502201151390.28769@pobox.suse.cz>
 <20150220194901.GB3603@gmail.com>
 <20150220214613.GA21598@suse.com>
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On Fri, Feb 20, 2015 at 10:46:13PM +0100, Vojtech Pavlik wrote:
> On Fri, Feb 20, 2015 at 08:49:01PM +0100, Ingo Molnar wrote:
> > I.e. it's in essence the strong stop-all atomic patching 
> > model of 'kpatch', combined with the reliable avoidance of 
> > kernel stacks that 'kgraft' uses.
> 
> > That should be the starting point, because it's the most 
> > reliable method.
> 
> In the consistency models discussion, this was marked the
> "LEAVE_KERNEL+SWITCH_KERNEL" model. It's indeed the strongest model of
> all, but also comes at the highest cost in terms of impact on running
> tasks. It's so high (the interruption may be seconds or more) that it
> was deemed not worth implementing.

Yeah, this is way too disruptive to the user.

Even the comparatively tiny latency caused by kpatch's use of
stop_machine() was considered unacceptable by some.

Plus a lot of processes would see EINTR, causing more havoc.

-- 
Josh
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