linux-kernel - Re: [PATCH] slub: Disable the lockless allocator

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Date:	Sun, 27 Mar 2011 09:52:27 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Pekka Enberg <penberg@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	akpm@...ux-foundation.org, tj@...nel.org, npiggin@...nel.dk,
	rientjes@...gle.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] slub: Disable the lockless allocator

Le samedi 26 mars 2011 à 20:57 -0500, Christoph Lameter a écrit :
> But then the same fix must also be used in the asm code or the fallback
> (turns out that the fallback is always used in kmem_cache_init since
> the instruction patching comes later).
> 
> Patch boots fine both in UP and SMP mode
> 
> 
> 
> 
> Subject: percpu: Omit segment prefix in the UP case for cmpxchg_double
> 
> Omit the segment prefix in the UP case. GS is not used then
> and we will generate segfaults if cmpxchg16b is used otherwise.
> 
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Christoph Lameter <cl@...ux.com>
> 
>  arch/x86/include/asm/percpu.h |   10 ++++++----
>  1 files changed, 6 insertions(+), 4 deletions(-)
> 
> Index: linux-2.6/arch/x86/include/asm/percpu.h
> ===================================================================
> --- linux-2.6.orig/arch/x86/include/asm/percpu.h	2011-03-26 20:43:03.994089001 -0500
> +++ linux-2.6/arch/x86/include/asm/percpu.h	2011-03-26 20:43:22.414089004 -0500
> @@ -45,7 +45,7 @@
>  #include <linux/stringify.h>
> 
>  #ifdef CONFIG_SMP
> -#define __percpu_arg(x)		"%%"__stringify(__percpu_seg)":%P" #x
> +#define __percpu_prefix		"%%"__stringify(__percpu_seg)":"
>  #define __my_cpu_offset		percpu_read(this_cpu_off)
> 
>  /*
> @@ -62,9 +62,11 @@
>  	(typeof(*(ptr)) __kernel __force *)tcp_ptr__;	\
>  })
>  #else
> -#define __percpu_arg(x)		"%P" #x
> +#define __percpu_prefix		""
>  #endif
> 
> +#define __percpu_arg(x)		__percpu_prefix "%P" #x
> +
>  /*
>   * Initialized pointers to per-cpu variables needed for the boot
>   * processor need to use these macros to get the proper address
> @@ -516,11 +518,11 @@
>  	typeof(o2) __n2 = n2;						\
>  	typeof(o2) __dummy;						\
>  	alternative_io("call this_cpu_cmpxchg16b_emu\n\t" P6_NOP4,	\

I guess you should make P6_NOP4 be P6_NOP3 in !SMP builds.

> -		       "cmpxchg16b %%gs:(%%rsi)\n\tsetz %0\n\t",	\
> +		       "cmpxchg16b " __percpu_prefix "(%%rsi)\n\tsetz %0\n\t",	\
>  		       X86_FEATURE_CX16,				\
>  		       ASM_OUTPUT2("=a"(__ret), "=d"(__dummy)),		\
>  		       "S" (&pcp1), "b"(__n1), "c"(__n2),		\
> -		       "a"(__o1), "d"(__o2));				\
> +		       "a"(__o1), "d"(__o2) : "memory");		\
>  	__ret;								\
>  })
> 



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