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Date:   Thu, 23 Jan 2020 21:02:02 -0800
From:   Matthew Wilcox <willy@infradead.org>
To:     Qian Cai <cai@lca.pw>
Cc:     Peter Zijlstra <peterz@infradead.org>, mingo@redhat.com,
        juri.lelli@redhat.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, paulmck@kernel.org, tglx@linutronix.de,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linux-alpha@vger.kernel.org, Matt Turner <mattst88@gmail.com>,
        linux-parisc@vger.kernel.org, Helge Deller <deller@gmx.de>
Subject: Re: [PATCH v2] sched/core: fix illegal RCU from offline CPUs
Message-ID: <20200124050202.GJ4675@bombadil.infradead.org>
References: <20200121103506.GH14914@hirez.programming.kicks-ass.net>
 <A72A7F42-A166-4403-B12C-32B2D7A662C4@lca.pw>
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On Thu, Jan 23, 2020 at 11:21:35PM -0500, Qian Cai wrote:
> > On Jan 21, 2020, at 5:35 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > 
> > Something like this; except you'll need to go audit archs to make sure
> > they all call idle_task_exit() and/or put in comments on why they don't
> > have to (perhaps their bringup switches them to &init_mm unconditionally
> > and the switch_mm() is not required).
> 
> Damn, I am having a hard time to motivate myself to learn all about those two “dead“ arches from scratch. I suppose the first step we could put a dummy finish_cpu() for alpha and parisc if they don’t call idle_task_exit() in the first place anyway, so if it is a bug there it is another issue that could be dealt with in a separate patch later?

Or you could consult the maintainers of those architectures?  There are regular pull requests for parisc still, and alpha still gets odd fixes.

It would have helped had you not trimmed the context so aggressively.
For those seeing this thread for the first time, try:
https://lore.kernel.org/linux-mm/A72A7F42-A166-4403-B12C-32B2D7A662C4@lca.pw/T/#t