From: =?utf-8?Q?Lothar_Wa=C3=9Fmann?= <LW@KARO-electronics.de> To: <linux-kernel@vger.kernel.org> Cc: <linux-arm-kernel@lists.infradead.org>, Thomas Gleixner <tglx@linutronix.de> Subject: [BUG] genirq: Race condition in ONESHOT IRQ handler disabling IRQ forever Date: Mon, 6 Feb 2012 09:14:47 +0100 [thread overview] Message-ID: <20271.35831.227679.177366@ipc1.ka-ro> (raw) Hi, I already sent this to <linux-kernel@vger.kernel.org> on Feb. 1, 2012 but did not get any response there. So resending to a wider audience with improved subject line: there is a race condition in the threaded IRQ handler code for oneshot interrupts that may lead to disabling an IRQ indefinitely. IRQs are masked before calling the hard-irq handler and are unmasked only after the soft-irq handler has been run. Thus if the hard-irq handler returns IRQ_HANDLED instead of IRQ_WAKE_THREAD, meaning the soft-irq will not be called, the interrupt will remain masked forever. This can happen due to a short pulse on the interrupt line, that triggers the interrupt logic, but goes undetected by the hard-irq handler. The problem can be reproduced with the TSC2007 touch controller driver that uses ONESHOT interrupts. The problem arises also with interrupt controllers that latch a level triggered IRQ until it is acknowledged (like the i.MX28 does). In this case the IRQ status bit will remain asserted after the soft-irq finishes and retrigger the interrupt while the interrupt line is already deasserted. The following patch would solve the problem, but I'm not sure whether it's the Right Thing(TM) to do. Especially wrt. shared interrupts. diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c index 470d08c..93beadb 100644 --- a/kernel/irq/handle.c +++ b/kernel/irq/handle.c @@ -146,6 +146,11 @@ handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action) /* Fall through to add to randomness */ case IRQ_HANDLED: random |= action->flags; + /* unmask the IRQ that has been left masked + * due to race condition + */ + if (res == IRQ_HANDLED && (action->flags & IRQF_ONESHOT)) + unmask_irq(desc); break; default: Best regards, Lothar Wassmann -- ___________________________________________________________ Ka-Ro electronics GmbH | Pascalstraße 22 | D - 52076 Aachen Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10 Geschäftsführer: Matthias Kaussen Handelsregistereintrag: Amtsgericht Aachen, HRB 4996 www.karo-electronics.de | info@karo-electronics.de ___________________________________________________________
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From: LW@KARO-electronics.de (=?utf-8?Q?Lothar_Wa=C3=9Fmann?=) To: linux-arm-kernel@lists.infradead.org Subject: [BUG] genirq: Race condition in ONESHOT IRQ handler disabling IRQ forever Date: Mon, 6 Feb 2012 09:14:47 +0100 [thread overview] Message-ID: <20271.35831.227679.177366@ipc1.ka-ro> (raw) Hi, I already sent this to <linux-kernel@vger.kernel.org> on Feb. 1, 2012 but did not get any response there. So resending to a wider audience with improved subject line: there is a race condition in the threaded IRQ handler code for oneshot interrupts that may lead to disabling an IRQ indefinitely. IRQs are masked before calling the hard-irq handler and are unmasked only after the soft-irq handler has been run. Thus if the hard-irq handler returns IRQ_HANDLED instead of IRQ_WAKE_THREAD, meaning the soft-irq will not be called, the interrupt will remain masked forever. This can happen due to a short pulse on the interrupt line, that triggers the interrupt logic, but goes undetected by the hard-irq handler. The problem can be reproduced with the TSC2007 touch controller driver that uses ONESHOT interrupts. The problem arises also with interrupt controllers that latch a level triggered IRQ until it is acknowledged (like the i.MX28 does). In this case the IRQ status bit will remain asserted after the soft-irq finishes and retrigger the interrupt while the interrupt line is already deasserted. The following patch would solve the problem, but I'm not sure whether it's the Right Thing(TM) to do. Especially wrt. shared interrupts. diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c index 470d08c..93beadb 100644 --- a/kernel/irq/handle.c +++ b/kernel/irq/handle.c @@ -146,6 +146,11 @@ handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action) /* Fall through to add to randomness */ case IRQ_HANDLED: random |= action->flags; + /* unmask the IRQ that has been left masked + * due to race condition + */ + if (res == IRQ_HANDLED && (action->flags & IRQF_ONESHOT)) + unmask_irq(desc); break; default: Best regards, Lothar Wassmann -- ___________________________________________________________ Ka-Ro electronics GmbH | Pascalstra?e 22 | D - 52076 Aachen Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10 Gesch?ftsf?hrer: Matthias Kaussen Handelsregistereintrag: Amtsgericht Aachen, HRB 4996 www.karo-electronics.de | info at karo-electronics.de ___________________________________________________________
next reply other threads:[~2012-02-06 8:14 UTC|newest] Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top 2012-02-06 8:14 =?utf-8?Q?Lothar_Wa=C3=9Fmann?= [this message] 2012-02-06 8:14 ` [BUG] genirq: Race condition in ONESHOT IRQ handler disabling IRQ forever =?utf-8?Q?Lothar_Wa=C3=9Fmann?= 2012-02-06 10:42 ` Lars-Peter Clausen 2012-02-06 10:42 ` Lars-Peter Clausen 2012-02-07 9:03 ` Yong Zhang 2012-02-07 9:03 ` Yong Zhang 2012-02-07 10:01 ` Lothar Waßmann 2012-02-07 10:01 ` Lothar Waßmann 2012-02-07 12:34 ` Yong Zhang 2012-02-07 12:34 ` Yong Zhang 2012-02-07 12:52 ` Lothar Waßmann 2012-02-07 12:52 ` Lothar Waßmann 2012-02-07 13:07 ` Lars-Peter Clausen 2012-02-07 13:07 ` Lars-Peter Clausen 2012-02-07 13:38 ` [PATCH] genirq: Fix race condition in ONESHOT irq handler Lothar Waßmann 2012-02-07 13:38 ` Lothar Waßmann 2012-02-07 17:03 ` Thomas Gleixner 2012-02-07 17:03 ` Thomas Gleixner 2012-02-08 6:05 ` Lothar Waßmann 2012-02-08 6:05 ` Lothar Waßmann 2012-02-08 10:38 ` Thomas Gleixner 2012-02-08 10:38 ` Thomas Gleixner 2012-02-09 8:40 ` Lothar Waßmann 2012-02-09 8:40 ` Lothar Waßmann
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