linux-kernel - Re: [RFC] sched,livepatch: call klp_try_switch_task in __cond

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Message-ID: <bf682c8874a044a643becbb8704a4dfedadc3321.camel@fb.com>
Date:   Wed, 11 May 2022 00:46:32 +0000
From:   Rik van Riel <riel@...com>
To:     "jpoimboe@...nel.org" <jpoimboe@...nel.org>
CC:     "song@...nel.org" <song@...nel.org>,
        "joe.lawrence@...hat.com" <joe.lawrence@...hat.com>,
        Song Liu <songliubraving@...com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
        "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        Kernel Team <Kernel-team@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pmladek@...e.com" <pmladek@...e.com>
Subject: Re: [RFC] sched,livepatch: call klp_try_switch_task in __cond_resched

On Tue, 2022-05-10 at 17:37 -0700, Josh Poimboeuf wrote:
> On Wed, May 11, 2022 at 12:35:11AM +0000, Rik van Riel wrote:
> > On Tue, 2022-05-10 at 23:57 +0000, Song Liu wrote:
> > > 
> > > So, if we come back to the same question: is this a bug (or a
> > > suboptimal
> > > behavior that worth fixing)? If so, we are open to any solution
> > > that 
> > > would also help PREEMPT and/or non-x86 arches. 
> > > 
> > Using the preempt notifiers during KLP transition should
> > work equally well for PREEMPT and !PREEMPT. It also does
> > not insert any additional code into the scheduler while
> > there is no KLP transition going on.
> 
> As I've been saying, this is not going to work for PREEMPT because,
> without ORC, we can't reliably unwind from an IRQ handler, so the
> kthread won't get patched.
> 
Isn't the sched_out preempt notifier always run in
process context?

What am I missing?