linux-kernel - Re: [GIT pull] locking/urgent for v5.10-rc6

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Message-ID: <20201201184807.GN3092@hirez.programming.kicks-ass.net>
Date:   Tue, 1 Dec 2020 19:48:07 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [GIT pull] locking/urgent for v5.10-rc6

On Tue, Dec 01, 2020 at 07:15:06PM +0100, Peter Zijlstra wrote:
> On Tue, Dec 01, 2020 at 03:55:19PM +0100, Peter Zijlstra wrote:
> > On Tue, Dec 01, 2020 at 06:46:44AM -0800, Paul E. McKenney wrote:
> > 
> > > > So after having talked to Sven a bit, the thing that is happening, is
> > > > that this is the one place where we take interrupts with RCU being
> > > > disabled. Normally RCU is watching and all is well, except during idle.
> > > 
> > > Isn't interrupt entry supposed to invoke rcu_irq_enter() at some point?
> > > Or did this fall victim to recent optimizations?
> > 
> > It does, but the problem is that s390 is still using
> 
> I might've been too quick there, I can't actually seem to find where
> s390 does rcu_irq_enter()/exit().

Argh, do_IRQ is per arch.. and that does irq_enter() which then does the
deed (thanks Sven!).