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Date: Wed, 26 Feb 2003 01:54:09 -0800
From: Andrew Morton <akpm@digeo.com>
To: Dave Jones <davej@codemonkey.org.uk>
Cc: schlicht@uni-mannheim.de, torvalds@transmeta.com, hugh@veritas.com,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH][2.5] fix preempt-issues with smp_call_function()
Message-Id: <20030226015409.78e8e1fb.akpm@digeo.com>
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	<20030226103742.GA29250@suse.de>
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Dave Jones <davej@codemonkey.org.uk> wrote:
>
> On Tue, Feb 25, 2003 at 07:08:48PM +0100, Thomas Schlichter wrote:
> 
>  > here is a patch to solve all (I hope I missed none) possible problems that 
>  > could occur on SMP machines running a preemptible kernel when 
>  > smp_call_function() calls a function which should be also executed on the 
>  > current processor.
>  > 
>  > This patch is based on the one Dave Jones sent to the LKML last friday and 
>  > applies to the linux kernel version 2.5.63.
> 
> Just one comment. You moved quite a few of the preempt_disable/enable
> pairs outside of the CONFIG_SMP checks.  The issue we're working against
> here is to try and prevent preemption and ending up on a different CPU.
> As this cannot happen if CONFIG_SMP=n, I don't see why you've done this.
> 

Just in two places.


 arch/i386/kernel/ldt.c   |    6 ++++--
 arch/x86_64/kernel/ldt.c |    6 ++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff -puN arch/i386/kernel/ldt.c~on_each_cpu-ldt-cleanup arch/i386/kernel/ldt.c
--- 25/arch/i386/kernel/ldt.c~on_each_cpu-ldt-cleanup	2003-02-26 01:51:27.000000000 -0800
+++ 25-akpm/arch/i386/kernel/ldt.c	2003-02-26 01:52:21.000000000 -0800
@@ -55,13 +55,15 @@ static int alloc_ldt(mm_context_t *pc, i
 	wmb();
 
 	if (reload) {
+#ifdef CONFIG_SMP
 		preempt_disable();
 		load_LDT(pc);
-#ifdef CONFIG_SMP
 		if (current->mm->cpu_vm_mask != (1 << smp_processor_id()))
 			smp_call_function(flush_ldt, 0, 1, 1);
-#endif
 		preempt_enable();
+#else
+		load_LDT(pc);
+#endif
 	}
 	if (oldsize) {
 		if (oldsize*LDT_ENTRY_SIZE > PAGE_SIZE)
diff -puN arch/x86_64/kernel/ldt.c~on_each_cpu-ldt-cleanup arch/x86_64/kernel/ldt.c
--- 25/arch/x86_64/kernel/ldt.c~on_each_cpu-ldt-cleanup	2003-02-26 01:51:36.000000000 -0800
+++ 25-akpm/arch/x86_64/kernel/ldt.c	2003-02-26 01:52:37.000000000 -0800
@@ -60,13 +60,15 @@ static int alloc_ldt(mm_context_t *pc, i
 	pc->size = mincount;
 	wmb();
 	if (reload) {
+#ifdef CONFIG_SMP
 		preempt_disable();
 		load_LDT(pc);
-#ifdef CONFIG_SMP
 		if (current->mm->cpu_vm_mask != (1<<smp_processor_id()))
 			smp_call_function(flush_ldt, 0, 1, 1);
-#endif
 		preempt_enable();
+#else
+		load_LDT(pc);
+#endif
 	}
 	if (oldsize) {
 		if (oldsize*LDT_ENTRY_SIZE > PAGE_SIZE)

_

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