linux-kernel - Re: [PATCH v3] ring-buffer: Race when writing and swapping cpu buffer in parallel

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Date:	Tue, 29 Jul 2014 11:02:34 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Petr Mládek <pmladek@...e.cz>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] ring-buffer: Race when writing and swapping cpu buffer
 in parallel

On Mon, 21 Jul 2014, Steven Rostedt wrote:

> > I thought that IPI used NMI and thus could not be blocked if the
> > called function was reasonable. Note that ring_buffer_swap_cpu() does not take
> > any lock and can't block anywhere. I am probably too optimistic here.
> 
> Heh, that would be a crazy system. No, IPI is a normal maskable
> interrupt. It does not use NMIs. In fact, IPI is how irq_work is
> implemented to do stuff from an NMI outside of NMI context.

Just for the sake of completness -- on x86, it is possible to send NMI IPI 
by simply doing

	apic->send_IPI_mask(mask, NMI_VECTOR);

but obviously smp_call_funcion_*() are not using this.

-- 
Jiri Kosina
SUSE Labs
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