From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 4 May 2010 02:21:42 +0200 From: Guillaume Knispel To: linux-kernel@vger.kernel.org, Linuxppc-dev@lists.ozlabs.org Subject: [PATCHv2 1/2] genirq: reliably replay pending edge-triggered irq Message-Id: <20100504022142.1eb653da.gknispel@proformatique.com> In-Reply-To: <20100504021941.ff7579c1.gknispel@proformatique.com> References: <20100504021941.ff7579c1.gknispel@proformatique.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Cc: Randy Dunlap , Lars-Peter Clausen , Russell King , Bartlomiej Zolnierkiewicz , Haavard Skinnemoen , Guillaume Knispel , Peter Zijlstra , Ingo Molnar , Linus Torvalds , Thomas Gleixner List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , The following can happen: CPU 1 CPU 2 disable_irq(): handle_edge_irq(): LOCK desc->lock (irqsave) desc->status |= IRQ_DISABLED; desc->chip->disable(irq);/*1*/ UNLOCK desc->lock (irqrestore) LOCK desc->lock desc->status |= (IRQ_PENDING | IRQ_MASKED); mask_ack_irq(desc, irq); UNLOCK desc->lock NOTE /*1*/: ->disable can point to default_disable(). Since commit: 76d2160147f43f982dfe881404cfde9fd0a9da21 genirq: do not mask interrupts by default the delayed interrupt disable mechanism has been activated for every user of default_disable() -- which used to mask the interrupt at controller level before and is now a noop. The sequence describing a race above will now indeed happen if an interrupt event occurs at any time between the effective disable_irq() and the next effective enable_irq(). Also note that even if ->disable does a masking, a similar race can indeed happen even on a monoprocessor system if an interrupt event occurs before just before the masking. In order to avoid interrupt loss, an IRQ_PENDING interrupt must be replayed when enable_irq() is called (or immediately after). This replay (implemented in kernel/irq/resend.c) used to be reliable only if: * the interrupt controller driver implements a reliable retrigger() callback or * CONFIG_HARDIRQS_SW_RESEND is defined (in this case the flow handler can be executed in a tasklet running resend_irqs() ) So CONFIG_HARDIRQS_SW_RESEND was meant to be set on plateforms where it exists a risk that edge interrupts are used on an interrupt controller that does not support hard retrigger (or at least not reliably). But CONFIG_HARDIRQS_SW_RESEND was only defined on arm and avr32 architectures, and other architectures exist which can have controllers without a reliable retrigger(). Some examples: * arch/powerpc/sysdev/cpm2.c arch/powerpc/sysdev/ipic.c * arch/blackfin/mach-common/ints-priority.c * arch/mips/alchemy/common/irq.c * ... With the present change, resend_irqs() is unconditionally built, so that edge-triggered interrupts can not be lost. The CONFIG_HARDIRQS_SW_RESEND option is not used anymore. See http://lkml.org/lkml/2010/4/19/129 for the first discussion about this problem. Signed-off-by: Guillaume Knispel CC: linux-kernel@vger.kernel.org CC: Linuxppc-dev@lists.ozlabs.org CC: Bartlomiej Zolnierkiewicz CC: Benjamin Herrenschmidt CC: Haavard Skinnemoen CC: Ingo Molnar CC: Lars-Peter Clausen CC: Linus Torvalds CC: Peter Zijlstra CC: Randy Dunlap CC: Russell King CC: Thomas Gleixner --- kernel/irq/resend.c | 6 ------ 1 files changed, 0 insertions(+), 6 deletions(-) diff --git a/kernel/irq/resend.c b/kernel/irq/resend.c index 090c376..3b20ce1 100644 --- a/kernel/irq/resend.c +++ b/kernel/irq/resend.c @@ -20,8 +20,6 @@ #include "internals.h" -#ifdef CONFIG_HARDIRQS_SW_RESEND - /* Bitmap to handle software resend of interrupts: */ static DECLARE_BITMAP(irqs_resend, NR_IRQS); @@ -46,8 +44,6 @@ static void resend_irqs(unsigned long arg) /* Tasklet to handle resend: */ static DECLARE_TASKLET(resend_tasklet, resend_irqs, 0); -#endif - /* * IRQ resend * @@ -71,11 +67,9 @@ void check_irq_resend(struct irq_desc *desc, unsigned int irq) desc->status = (status & ~IRQ_PENDING) | IRQ_REPLAY; if (!desc->chip->retrigger || !desc->chip->retrigger(irq)) { -#ifdef CONFIG_HARDIRQS_SW_RESEND /* Set it pending and activate the softirq: */ set_bit(irq, irqs_resend); tasklet_schedule(&resend_tasklet); -#endif } } } -- 1.6.2