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

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Date:   Wed, 2 Dec 2020 13:27:34 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        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 Wed, Dec 02, 2020 at 11:56:49AM +0100, Heiko Carstens wrote:
> From 7bd86fb3eb039a4163281472ca79b9158e726526 Mon Sep 17 00:00:00 2001
> From: Heiko Carstens <hca@...ux.ibm.com>
> Date: Wed, 2 Dec 2020 11:46:01 +0100
> Subject: [PATCH] s390: fix irq state tracing
> 
> With commit 58c644ba512c ("sched/idle: Fix arch_cpu_idle() vs
> tracing") common code calls arch_cpu_idle() with a lockdep state that
> tells irqs are on.
> 
> This doesn't work very well for s390: psw_idle() will enable interrupts
> to wait for an interrupt. As soon as an interrupt occurs the interrupt
> handler will verify if the old context was psw_idle(). If that is the
> case the interrupt enablement bits in the old program status word will
> be cleared.
> 
> A subsequent test in both the external as well as the io interrupt
> handler checks if in the old context interrupts were enabled. Due to
> the above patching of the old program status word it is assumed the
> old context had interrupts disabled, and therefore a call to
> TRACE_IRQS_OFF (aka trace_hardirqs_off_caller) is skipped. Which in
> turn makes lockdep incorrectly "think" that interrupts are enabled
> within the interrupt handler.
> 
> Fix this by unconditionally calling TRACE_IRQS_OFF when entering
> interrupt handlers. Also call unconditionally TRACE_IRQS_ON when
> leaving interrupts handlers.
> 
> This leaves the special psw_idle() case, which now returns with
> interrupts disabled, but has an "irqs on" lockdep state. So callers of
> psw_idle() must adjust the state on their own, if required. This is
> currently only __udelay_disabled().
> 
> Fixes: 58c644ba512c ("sched/idle: Fix arch_cpu_idle() vs tracing")
> Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>

Thanks for sorting this Heiko!

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>