linux-kernel - Re: [PATCH v5 1/1] MIPS: Fix idle VS timer enqueue

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Message-ID: <Z8G7ABDyvMPAx47Q@localhost.localdomain>
Date: Fri, 28 Feb 2025 14:32:48 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Marco Crivellari <marco.crivellari@...e.com>
Cc: linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Huacai Chen <chenhuacai@...nel.org>,
	"Maciej W . Rozycki" <macro@...am.me.uk>
Subject: Re: [PATCH v5 1/1] MIPS: Fix idle VS timer enqueue

Le Fri, Feb 28, 2025 at 11:05:09AM +0100, Marco Crivellari a écrit :
> MIPS re-enables interrupts on its idle routine and performs
> a TIF_NEED_RESCHED check afterwards before putting the CPU to sleep.
> 
> The IRQs firing between the check and the 'wait' instruction may set the
> TIF_NEED_RESCHED flag. In order to deal with this possible race, IRQs
> interrupting __r4k_wait() rollback their return address to the
> beginning of __r4k_wait() so that TIF_NEED_RESCHED is checked
> again before going back to sleep.
> 
> However idle IRQs can also queue timers that may require a tick
> reprogramming through a new generic idle loop iteration but those timers
> would go unnoticed here because __r4k_wait() only checks
> TIF_NEED_RESCHED. It doesn't check for pending timers.
> 
> Fix this with fast-forwarding idle IRQs return address to the end of the
> idle routine instead of the beginning, so that the generic idle loop
> handles both TIF_NEED_RESCHED and pending timers.
> 
> CONFIG_CPU_MICROMIPS has been removed along with the nop instructions.
> There, NOPs are 2 byte in size, so change the code with 3 _ssnop which are
> always 4 byte and remove the ifdef. Added ehb to make sure the hazard
> is always cleared.
> 
> Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>

Acked-by: Frederic Weisbecker <frederic@...nel.org>