linux-kernel - Re: [PATCH 1/2] sched/idle: Fix arch_cpu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20201201133846.GA26973@willie-the-truck>
Date:   Tue, 1 Dec 2020 13:38:47 +0000
From:   Will Deacon <will@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Sven Schnelle <svens@...ux.ibm.com>,
        Guenter Roeck <linux@...ck-us.net>, rafael@...nel.org,
        viresh.kumar@...aro.org, mingo@...nel.org, x86@...nel.org,
        mark.rutland@....com, linux-kernel@...r.kernel.org,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        linux-s390@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/2] sched/idle: Fix arch_cpu_idle() vs tracing

On Tue, Dec 01, 2020 at 01:52:46PM +0100, Peter Zijlstra wrote:
> On Tue, Dec 01, 2020 at 12:56:27PM +0100, Sven Schnelle wrote:
> > Peter Zijlstra <peterz@...radead.org> writes:
> > > On Mon, Nov 30, 2020 at 01:00:03PM -0800, Guenter Roeck wrote:
> > >> On Fri, Nov 20, 2020 at 12:41:46PM +0100, Peter Zijlstra wrote:
> > >> > 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)
> > >> > 
> > >> 
> > >> Has this patch been tested on s390 ? Reason for asking is that it causes
> > >> all my s390 emulations to crash. Reverting it fixes the problem.
> > >
> > > My understanding is that it changes the error on s390. Previously it
> > > would complain about the local_irq_enable() in arch_cpu_idle(), now it
> > > complains when taking an interrupt during idle.
> > 
> > I looked into adding the required functionality for s390, but the code
> > we would need to add to entry.S is rather large - as you noted we would
> > have to duplicate large portions of irqentry_enter() into our code.
> > Given that s390 was fine before that patch, can you revert it and submit
> > it again during the next merge window?
> 
> I'm not sure I understand how s390 was fine without it, let me consdier.
> Also, what's the status of ARM64, they do need this too.

We've got the batch of fixes from Mark queued for -rc7:

https://fixes.arm64.dev/

which rely on Peter's patch:

https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?h=for-next/fixes&id=114e0a684753516ef4b71ccb55a8ebcfa8735edb

There's room for consolidation and cleanup in future, but right now we've
focussed purely on fixing things.

Will