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[PATCH] synchronize_irq needs a barrier

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From: Benjamin Herrenschmidt <benh@...>
To: Linus Torvalds <torvalds@...>
Cc: akpm <akpm@...>, Linux Kernel list <linux-kernel@...>, linuxppc-dev list <linuxppc-dev@...>
Subject: [PATCH] synchronize_irq needs a barrier
Date: Wednesday, October 17, 2007 - 9:25 pm

synchronize_irq needs at the very least a compiler barrier and a
read barrier on SMP, but there are enough cases around where a
write barrier is also needed and it's not a hot path so I prefer
using a full smp_mb() here.

It will degrade to a compiler barrier on !SMP.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

Index: linux-work/kernel/irq/manage.c
===================================================================
--- linux-work.orig/kernel/irq/manage.c	2007-10-18 11:22:16.000000000 +1000
+++ linux-work/kernel/irq/manage.c	2007-10-18 11:22:20.000000000 +1000
@@ -33,6 +33,7 @@ void synchronize_irq(unsigned int irq)
 	if (irq >= NR_IRQS)
 		return;
 
+	smp_mb();
 	while (desc->status & IRQ_INPROGRESS)
 		cpu_relax();
 }


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Messages in current thread:
[PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Wed Oct 17, 9:25 pm)
Re: [PATCH] synchronize_irq needs a barrier, Maxim Levitsky, (Fri Oct 19, 10:02 pm)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Fri Oct 19, 11:56 pm)
Re: [PATCH] synchronize_irq needs a barrier, Maxim Levitsky, (Sat Oct 20, 12:24 am)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Sat Oct 20, 1:04 am)
Re: [PATCH] synchronize_irq needs a barrier, Maxim Levitsky, (Sat Oct 20, 1:36 am)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Sat Oct 20, 1:46 am)
Re: [PATCH] synchronize_irq needs a barrier, Maxim Levitsky, (Sat Oct 20, 2:06 am)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Sat Oct 20, 2:13 am)
Re: [PATCH] synchronize_irq needs a barrier, Herbert Xu, (Fri Oct 19, 11:37 pm)
Re: [PATCH] synchronize_irq needs a barrier, Linus Torvalds, (Fri Oct 19, 10:25 pm)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Sat Oct 20, 12:04 am)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Sat Oct 20, 12:09 am)
Re: [PATCH] synchronize_irq needs a barrier, Maxim Levitsky, (Fri Oct 19, 11:10 pm)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Sat Oct 20, 12:06 am)
Re: [PATCH] synchronize_irq needs a barrier, Linus Torvalds, (Wed Oct 17, 10:12 pm)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Wed Oct 17, 10:40 pm)
Re: [PATCH] synchronize_irq needs a barrier, Herbert Xu, (Thu Oct 18, 10:35 am)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Thu Oct 18, 5:35 pm)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Wed Oct 17, 10:57 pm)
Re: [PATCH] synchronize_irq needs a barrier, Herbert Xu, (Thu Oct 18, 10:56 am)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Thu Oct 18, 6:05 pm)
Re: [PATCH] synchronize_irq needs a barrier, Linus Torvalds, (Thu Oct 18, 6:52 pm)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Thu Oct 18, 7:17 pm)
Re: [PATCH] synchronize_irq needs a barrier, Linus Torvalds, (Thu Oct 18, 7:39 pm)
Re: [PATCH] synchronize_irq needs a barrier, Herbert Xu, (Thu Oct 18, 10:32 pm)
Re: [PATCH] synchronize_irq needs a barrier, Linus Torvalds, (Thu Oct 18, 10:55 pm)
Re: [PATCH] synchronize_irq needs a barrier, Linus Torvalds, (Thu Oct 18, 11:26 pm)
Re: [PATCH] synchronize_irq needs a barrier, Herbert Xu, (Fri Oct 19, 12:20 am)
[NET]: Fix possible dev_deactivate race condition, Herbert Xu, (Fri Oct 19, 1:36 am)
Re: [NET]: Fix possible dev_deactivate race condition, Peter Zijlstra, (Fri Oct 19, 3:35 am)
Re: [NET]: Fix possible dev_deactivate race condition, Herbert Xu, (Fri Oct 19, 5:29 am)
Re: [NET]: Fix possible dev_deactivate race condition, David Miller, (Fri Oct 19, 1:38 am)
Re: [PATCH] synchronize_irq needs a barrier, Herbert Xu, (Fri Oct 19, 12:48 am)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Fri Oct 19, 12:58 am)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Sun Oct 21, 5:10 pm)
[IRQ]: Fix synchronize_irq races with IRQ handler, Herbert Xu, (Mon Oct 22, 11:26 pm)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Fri Oct 19, 12:35 am)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Fri Oct 19, 12:29 am)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Fri Oct 19, 12:11 am)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Fri Oct 19, 12:26 am)
Re: [PATCH] synchronize_irq needs a barrier, Herbert Xu, (Fri Oct 19, 1:53 am)
Re: [PATCH] synchronize_irq needs a barrier, Nick Piggin, (Thu Oct 18, 10:52 pm)
Re: [PATCH] synchronize_irq needs a barrier, Herbert Xu, (Thu Oct 18, 11:28 pm)
Re: [PATCH] synchronize_irq needs a barrier, Nick Piggin, (Fri Oct 19, 12:49 am)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Thu Oct 18, 7:52 pm)
Re: [PATCH] synchronize_irq needs a barrier, Andrew Morton, (Wed Oct 17, 9:45 pm)
Re: [PATCH] synchronize_irq needs a barrier, Benjamin Herrenschmidt, (Wed Oct 17, 9:55 pm)