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

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Date:   Tue, 10 May 2022 17:37:16 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Rik van Riel <riel@...com>
Cc:     Song Liu <songliubraving@...com>,
        "song@...nel.org" <song@...nel.org>,
        "joe.lawrence@...hat.com" <joe.lawrence@...hat.com>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.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>,
        Kernel Team <Kernel-team@...com>,
        "pmladek@...e.com" <pmladek@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] sched,livepatch: call klp_try_switch_task in __cond_resched

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.

-- 
Josh