linux-kernel - Re: [PATCH -tip 3/4]Text Edit Lock

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Date:	Fri, 6 Mar 2009 13:11:33 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH -tip 3/4]Text Edit Lock - Smp alternatives support

* Masami Hiramatsu (mhiramat@...hat.com) wrote:
> Use the mutual exclusion provided by the text edit lock in alternatives code.
> Since alternative_smp_* will be called from module init code, etc,
> we'd better protect it from other subsystems.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> Cc: Ingo Molnar <mingo@...e.hu>
> ---
>  arch/x86/kernel/alternative.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> Index: 2.6.29-rc7/arch/x86/kernel/alternative.c
> ===================================================================
> --- 2.6.29-rc7.orig/arch/x86/kernel/alternative.c
> +++ 2.6.29-rc7/arch/x86/kernel/alternative.c
> @@ -5,6 +5,7 @@
>  #include <linux/kprobes.h>
>  #include <linux/mm.h>
>  #include <linux/vmalloc.h>
> +#include <linux/memory.h>
>  #include <asm/alternative.h>
>  #include <asm/sections.h>
>  #include <asm/pgtable.h>
> @@ -226,6 +227,7 @@ static void alternatives_smp_lock(u8 **s
>  {
>  	u8 **ptr;
> 
> +	mutex_lock(&text_mutex);
>  	for (ptr = start; ptr < end; ptr++) {
>  		if (*ptr < text)
>  			continue;
> @@ -234,6 +236,7 @@ static void alternatives_smp_lock(u8 **s
>  		/* turn DS segment override prefix into lock prefix */
>  		text_poke(*ptr, ((unsigned char []){0xf0}), 1);
>  	};
> +	mutex_unlock(&text_mutex);
>  }
> 
>  static void alternatives_smp_unlock(u8 **start, u8 **end, u8 *text, u8 *text_end)
> @@ -243,6 +246,7 @@ static void alternatives_smp_unlock(u8 *
>  	if (noreplace_smp)
>  		return;
> 
> +	mutex_lock(&text_mutex);
>  	for (ptr = start; ptr < end; ptr++) {
>  		if (*ptr < text)
>  			continue;
> @@ -251,6 +255,7 @@ static void alternatives_smp_unlock(u8 *
>  		/* turn lock prefix into DS segment override prefix */
>  		text_poke(*ptr, ((unsigned char []){0x3E}), 1);
>  	};
> +	mutex_unlock(&text_mutex);

And for these cases, the "alternatives_smp_lock" and
"alternatives_smp_unlock", the system is running as uniprocessor.
Therefore it's enough to disable interrupts within text_poke to make it
work correctly.

Mathieu

>  }
> 
>  struct smp_alt_module {
> -- 
> Masami Hiramatsu
> 
> Software Engineer
> Hitachi Computer Products (America) Inc.
> Software Solutions Division
> 
> e-mail: mhiramat@...hat.com
> 

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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