From: Guillaume Knispel <gknispel@proformatique•com>
To: linux-kernel@vger•kernel.org, Linuxppc-dev@lists•ozlabs.org
Cc: Randy Dunlap <randy.dunlap@oracle•com>,
Lars-Peter Clausen <lars@metafoo•de>,
Russell King <linux@arm•linux.org.uk>,
Bartlomiej Zolnierkiewicz <bzolnier@gmail•com>,
Haavard Skinnemoen <hskinnemoen@atmel•com>,
Guillaume Knispel <gknispel@proformatique•com>,
Peter Zijlstra <peterz@infradead•org>,
Ingo Molnar <mingo@elte•hu>,
Linus Torvalds <torvalds@linux-foundation•org>,
Thomas Gleixner <tglx@linutronix•de>
Subject: [PATCHv2 1/2] genirq: reliably replay pending edge-triggered irq
Date: Tue, 4 May 2010 02:21:42 +0200 [thread overview]
Message-ID: <20100504022142.1eb653da.gknispel@proformatique.com> (raw)
In-Reply-To: <20100504021941.ff7579c1.gknispel@proformatique.com>
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 <gknispel@proformatique•com>
CC: linux-kernel@vger•kernel.org
CC: Linuxppc-dev@lists•ozlabs.org
CC: Bartlomiej Zolnierkiewicz <bzolnier@gmail•com>
CC: Benjamin Herrenschmidt <benh@kernel•crashing.org>
CC: Haavard Skinnemoen <hskinnemoen@atmel•com>
CC: Ingo Molnar <mingo@elte•hu>
CC: Lars-Peter Clausen <lars@metafoo•de>
CC: Linus Torvalds <torvalds@linux-foundation•org>
CC: Peter Zijlstra <peterz@infradead•org>
CC: Randy Dunlap <randy.dunlap@oracle•com>
CC: Russell King <linux@arm•linux.org.uk>
CC: Thomas Gleixner <tglx@linutronix•de>
---
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
next prev parent reply other threads:[~2010-05-04 0:21 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-04 0:19 [PATCHv2 0/2] genirq: reliably replay pending edge-triggered irq (plus doc) Guillaume Knispel
2010-05-04 0:21 ` Guillaume Knispel [this message]
2010-05-04 0:23 ` [PATCHv2 2/2] genirq: update doc Guillaume Knispel
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20100504022142.1eb653da.gknispel@proformatique.com \
--to=gknispel@proformatique$(echo .)com \
--cc=Linuxppc-dev@lists$(echo .)ozlabs.org \
--cc=bzolnier@gmail$(echo .)com \
--cc=hskinnemoen@atmel$(echo .)com \
--cc=lars@metafoo$(echo .)de \
--cc=linux-kernel@vger$(echo .)kernel.org \
--cc=linux@arm$(echo .)linux.org.uk \
--cc=mingo@elte$(echo .)hu \
--cc=peterz@infradead$(echo .)org \
--cc=randy.dunlap@oracle$(echo .)com \
--cc=tglx@linutronix$(echo .)de \
--cc=torvalds@linux-foundation$(echo .)org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox