linux-kernel - Re: [PATCH v9 4/8] smp: add func to IPI cpus based on parameter func

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Message-Id: <20120209142625.0664e055.akpm@linux-foundation.org>
Date:	Thu, 9 Feb 2012 14:26:25 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
Cc:	linux-kernel@...r.kernel.org, Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Russell King <linux@....linux.org.uk>, linux-mm@...ck.org,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, Avi Kivity <avi@...hat.com>,
	Kosaki Motohiro <kosaki.motohiro@...il.com>,
	Milton Miller <miltonm@....com>
Subject: Re: [PATCH v9 4/8] smp: add func to IPI cpus based on parameter
 func

On Thu,  9 Feb 2012 10:36:21 +0200
Gilad Ben-Yossef <gilad@...yossef.com> wrote:

> @@ -153,6 +162,22 @@ static inline int up_smp_call_function(smp_call_func_t func, void *info)
>  			local_irq_enable();		\
>  		}					\
>  	} while (0)
> +/*
> + * Preemption is disabled here to make sure the
> + * cond_func is called under the same condtions in UP
> + * and SMP.
> + */
> +#define on_each_cpu_cond(cond_func, func, info, wait, gfp_flags) \
> +	do {
> +		void *__info = (info);			\
> +		preempt_disable();			\
> +		if ((cond_func)(0, __info)) {		\
> +			local_irq_disable();		\
> +			(func)(__info);			\
> +			local_irq_enable();		\
> +		}					\
> +		preempt_enable();			\
> +	} while (0)

That wasn't compile-tested!

This is one of the many reasons why I convert replacement patches into
incremental patches - so I can see what was done.

Here's what I queued after converting this patch into a delta:

--- a/kernel/smp.c~smp-add-func-to-ipi-cpus-based-on-parameter-func-v9
+++ a/kernel/smp.c
@@ -771,7 +771,9 @@ EXPORT_SYMBOL(on_each_cpu_mask);
  * The function might sleep if the GFP flags indicates a non
  * atomic allocation is allowed.
  *
- * Preemption is disabled to protect against a hotplug event.
+ * Preemption is disabled to protect against CPU going offline but not
+ * online. CPUs going online during the call will not be seen or sent
+ * an IPI.
  *
  * You must not call this function with disabled interrupts or
  * from a hardware interrupt handler or from a bottom half handler.
_

And I queued a small fix to that:

From: Andrew Morton <akpm@...ux-foundation.org>
Subject: smp-add-func-to-ipi-cpus-based-on-parameter-func-v9-fix

s/CPU/CPUs, use all 80 cols in comment

Cc: Gilad Ben-Yossef <gilad@...yossef.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 kernel/smp.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/kernel/smp.c~smp-add-func-to-ipi-cpus-based-on-parameter-func-v9-fix
+++ a/kernel/smp.c
@@ -771,9 +771,8 @@ EXPORT_SYMBOL(on_each_cpu_mask);
  * The function might sleep if the GFP flags indicates a non
  * atomic allocation is allowed.
  *
- * Preemption is disabled to protect against CPU going offline but not
- * online. CPUs going online during the call will not be seen or sent
- * an IPI.
+ * Preemption is disabled to protect against CPUs going offline but not online.
+ * CPUs going online during the call will not be seen or sent an IPI.
  *
  * You must not call this function with disabled interrupts or
  * from a hardware interrupt handler or from a bottom half handler.
_

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