linux-kernel - Re: [PATCH AUTOSEL 5.9 27/39] sched/idle: Fix arch_cpu

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Message-ID: <20201203171015.GN2414@hirez.programming.kicks-ass.net>
Date:   Thu, 3 Dec 2020 18:10:15 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Sven Schnelle <svens@...ux.ibm.com>,
        Mark Rutland <mark.rutland@....com>,
        linux-alpha@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-csky@...r.kernel.org, uclinux-h8-devel@...ts.sourceforge.jp,
        linux-hexagon@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-mips@...r.kernel.org, openrisc@...ts.librecores.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-um@...ts.infradead.org
Subject: Re: [PATCH AUTOSEL 5.9 27/39] sched/idle: Fix arch_cpu_idle() vs
 tracing

On Thu, Dec 03, 2020 at 03:54:42PM +0100, Heiko Carstens wrote:
> On Thu, Dec 03, 2020 at 08:28:21AM -0500, Sasha Levin wrote:
> > From: Peter Zijlstra <peterz@...radead.org>
> > 
> > [ Upstream commit 58c644ba512cfbc2e39b758dd979edd1d6d00e27 ]
> > 
> > We call arch_cpu_idle() with RCU disabled, but then use
> > local_irq_{en,dis}able(), which invokes tracing, which relies on RCU.
> > 
> > Switch all arch_cpu_idle() implementations to use
> > raw_local_irq_{en,dis}able() and carefully manage the
> > lockdep,rcu,tracing state like we do in entry.
> > 
> > (XXX: we really should change arch_cpu_idle() to not return with
> > interrupts enabled)
> > 
> > Reported-by: Sven Schnelle <svens@...ux.ibm.com>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > Reviewed-by: Mark Rutland <mark.rutland@....com>
> > Tested-by: Mark Rutland <mark.rutland@....com>
> > Link: https://lkml.kernel.org/r/20201120114925.594122626@infradead.org
> > Signed-off-by: Sasha Levin <sashal@...nel.org>
> 
> This patch broke s390 irq state tracing. A patch to fix this is
> scheduled to be merged upstream today (hopefully).
> Therefore I think this patch should not yet go into 5.9 stable.

Agreed.