Re: [PATCH] synchronize_irq needs a barrier
flat view
From: Andrew Morton <akpm@linux-foundation.org>
Date: 2007-10-18 01:45:28
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On Thu, 18 Oct 2007 11:25:42 +1000 Benjamin Herrenschmidt [off-list ref] wrote:
synchronize_irq needs at the very least a compiler barrier and a read barrier on SMP,
Why?
quoted hunk ↗ jump to hunk
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(); }
Anyone reading this code is going to ask "wtf is that for". It needs a comment telling them. mb() is the new lock_kernel(). Sigh.