Re: Irq handler reentrancy ?

[Robert Love <rml@tech9.net>]

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On Wed, 2002-09-04 at 18:18, Jean Tourrilhes wrote:

> 	Just a quick question : can an interrupt handler be preempted
> or reenter itself ?

It is not supposed to.

There is a bug in 2.5, with a fix from Linus currently in bitkeeper.  I
have attached the patch.

	Robert Love

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# This is a BitKeeper generated patch for the following project:
# Project Name: Linux kernel tree
# This patch format is intended for GNU patch command version 2.5 or higher.
# This patch includes the following deltas:
#	           ChangeSet	1.610   -> 1.611  
#	arch/i386/kernel/irq.c	1.17    -> 1.18   
#
# The following is the BitKeeper ChangeSet Log
# --------------------------------------------
# 02/09/04	torvalds@home.transmeta.com	1.611
# Fix IO-APIC edge IRQ handling. IRQ_INPROGRESS was cleared spuriously
# if a new edge happened while we were still processing the previous
# one.
# 
# Then, if a _third_ edge came in, it would actually cause a reentrant
# irq handler invocation, because the original INPROGRESS bit was now
# lost.
# 
# This was actually seen on IDE in PIO mode.
# --------------------------------------------
#
diff -Nru a/arch/i386/kernel/irq.c b/arch/i386/kernel/irq.c
--- a/arch/i386/kernel/irq.c	Wed Sep  4 12:00:11 2002
+++ b/arch/i386/kernel/irq.c	Wed Sep  4 12:00:11 2002
@@ -380,8 +380,9 @@
 			break;
 		desc->status &= ~IRQ_PENDING;
 	}
-out:
 	desc->status &= ~IRQ_INPROGRESS;
+
+out:
 	/*
 	 * The ->end() handler has to deal with interrupts which got
 	 * disabled while the handler was running.
@@ -768,7 +769,7 @@
 
 	if (!shared) {
 		desc->depth = 0;
-		desc->status &= ~(IRQ_DISABLED | IRQ_AUTODETECT | IRQ_WAITING);
+		desc->status &= ~(IRQ_DISABLED | IRQ_AUTODETECT | IRQ_WAITING | IRQ_INPROGRESS);
 		desc->handler->startup(irq);
 	}
 	spin_unlock_irqrestore(&desc->lock,flags);