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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id w123sm426385pfb.109.2021.06.02.14.05.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Jun 2021 14:05:26 -0700 (PDT) Date: Wed, 2 Jun 2021 14:05:25 -0700 From: Kees Cook To: Tanner Love Cc: linux-kernel@vger.kernel.org, "David S . Miller" , Eric Dumazet , Willem de Bruijn , Thomas Gleixner , Peter Zijlstra , Greg Kroah-Hartman , John Garry , Barry Song , Romain Perier , Tanner Love Subject: Re: [PATCH] genirq: change force_irqthreads from bool test to static key Message-ID: <202106021402.C7D3331@keescook> References: <20210602180338.3324213-1-tannerlove.kernel@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210602180338.3324213-1-tannerlove.kernel@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 02, 2021 at 02:03:38PM -0400, Tanner Love wrote: > From: Tanner Love > > With CONFIG_IRQ_FORCED_THREADING=y, testing the bool force_irqthreads > could incur a cache line miss in invoke_softirq(). > > Replace the test with a static key to avoid the potential cache miss. > > Suggested-by: Eric Dumazet > Signed-off-by: Tanner Love > Reviewed-by: Eric Dumazet > --- > drivers/ide/ide-iops.c | 7 +++---- > include/linux/interrupt.h | 4 +++- > kernel/irq/manage.c | 6 +++--- > 3 files changed, 9 insertions(+), 8 deletions(-) > > diff --git a/drivers/ide/ide-iops.c b/drivers/ide/ide-iops.c > index f2be127ee96e..f86cdb8451e6 100644 > --- a/drivers/ide/ide-iops.c > +++ b/drivers/ide/ide-iops.c > @@ -109,7 +109,6 @@ int __ide_wait_stat(ide_drive_t *drive, u8 good, u8 bad, > ide_hwif_t *hwif = drive->hwif; > const struct ide_tp_ops *tp_ops = hwif->tp_ops; > unsigned long flags; > - bool irqs_threaded = force_irqthreads; > int i; > u8 stat; > > @@ -117,7 +116,7 @@ int __ide_wait_stat(ide_drive_t *drive, u8 good, u8 bad, > stat = tp_ops->read_status(hwif); > > if (stat & ATA_BUSY) { > - if (!irqs_threaded) { > + if (!force_irqthreads) { > local_save_flags(flags); > local_irq_enable_in_hardirq(); > } > @@ -133,13 +132,13 @@ int __ide_wait_stat(ide_drive_t *drive, u8 good, u8 bad, > if ((stat & ATA_BUSY) == 0) > break; > > - if (!irqs_threaded) > + if (!force_irqthreads) > local_irq_restore(flags); > *rstat = stat; > return -EBUSY; > } > } > - if (!irqs_threaded) > + if (!force_irqthreads) > local_irq_restore(flags); > } > /* > diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h > index 4777850a6dc7..9e676c351f23 100644 > --- a/include/linux/interrupt.h > +++ b/include/linux/interrupt.h > @@ -13,6 +13,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -504,7 +505,8 @@ extern int irq_set_irqchip_state(unsigned int irq, enum irqchip_irq_state which, > # ifdef CONFIG_PREEMPT_RT > # define force_irqthreads (true) > # else > -extern bool force_irqthreads; > +DECLARE_STATIC_KEY_FALSE(force_irqthreads_key); > +# define force_irqthreads (static_branch_unlikely(&force_irqthreads_key)) I like this idiom, though it did make me look twice because I thought you were missing the static_branch...() calls above. ;) Reviewed-by: Kees Cook -Kees > # endif > #else > #define force_irqthreads (0) > diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c > index 4c14356543d9..395945e54929 100644 > --- a/kernel/irq/manage.c > +++ b/kernel/irq/manage.c > @@ -25,12 +25,12 @@ > #include "internals.h" > > #if defined(CONFIG_IRQ_FORCED_THREADING) && !defined(CONFIG_PREEMPT_RT) > -__read_mostly bool force_irqthreads; > -EXPORT_SYMBOL_GPL(force_irqthreads); > +DEFINE_STATIC_KEY_FALSE(force_irqthreads_key); > +EXPORT_SYMBOL_GPL(force_irqthreads_key); > > static int __init setup_forced_irqthreads(char *arg) > { > - force_irqthreads = true; > + static_branch_enable(&force_irqthreads_key); > return 0; > } > early_param("threadirqs", setup_forced_irqthreads); > -- > 2.32.0.rc0.204.g9fa02ecfa5-goog > -- Kees Cook