From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 487F5B7006 for ; Thu, 28 Jun 2012 17:10:49 +1000 (EST) Message-ID: <1340867444.20977.66.camel@pasglop> Subject: Re: [PATCH] powerpc: check_and_cede_processor never cedes From: Benjamin Herrenschmidt To: Anton Blanchard Date: Thu, 28 Jun 2012 17:10:44 +1000 In-Reply-To: <20120628091352.48d3859d@kryten> References: <20120628084509.4caec81d@kryten> <1340837479.3732.90.camel@pasglop> <20120628091352.48d3859d@kryten> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Cc: linuxppc-dev@lists.ozlabs.org, paulus@samba.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, 2012-06-28 at 09:13 +1000, Anton Blanchard wrote: > Hi, > > > I'd rather add a helper, something like lazy_irq_pending() > > and hide the actual check for the bits in irq_happened, in > > case we change the scheme again. > > Good idea. Look ok? > > -- > > Commit f948501b36c6 ("Make hard_irq_disable() actually hard-disable > interrupts") caused check_and_cede_processor to stop working. > ->irq_happened will never be zero right after a hard_irq_disable > so the compiler removes the call to cede_processor completely. > > The bug was introduced back in the lazy interrupt handling rework > of 3.4 but was hidden until recently because hard_irq_disable did > nothing. > > This issue will eventually appear in 3.4 stable since the > hard_irq_disable fix is marked stable, so mark this one for stable > too. Yup, looks good, I'll send to Linus tomorrow. Cheers, Ben. > Signed-off-by: Anton Blanchard > Cc: stable@vger.kernel.org > --- > > v2: create a helper, suggested by Ben. > > Index: linux-build/arch/powerpc/platforms/pseries/processor_idle.c > =================================================================== > --- linux-build.orig/arch/powerpc/platforms/pseries/processor_idle.c 2012-06-28 08:55:09.422198154 +1000 > +++ linux-build/arch/powerpc/platforms/pseries/processor_idle.c 2012-06-28 08:57:36.112591023 +1000 > @@ -106,7 +106,7 @@ static void check_and_cede_processor(voi > * we first hard disable then check. > */ > hard_irq_disable(); > - if (get_paca()->irq_happened == 0) > + if (!lazy_irq_pending()) > cede_processor(); > } > > Index: linux-build/arch/powerpc/include/asm/hw_irq.h > =================================================================== > --- linux-build.orig/arch/powerpc/include/asm/hw_irq.h 2012-06-21 09:16:26.265354429 +1000 > +++ linux-build/arch/powerpc/include/asm/hw_irq.h 2012-06-28 08:59:22.082320381 +1000 > @@ -103,6 +103,11 @@ static inline void hard_irq_disable(void > /* include/linux/interrupt.h needs hard_irq_disable to be a macro */ > #define hard_irq_disable hard_irq_disable > > +static inline bool lazy_irq_pending(void) > +{ > + return !!(get_paca()->irq_happened & ~PACA_IRQ_HARD_DIS); > +} > + > /* > * This is called by asynchronous interrupts to conditionally > * re-enable hard interrupts when soft-disabled after having