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Date: Tue, 07 Feb 2006 17:25:52 +0100
From: Eric Dumazet <dada1@cosmosbay.com>
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To: Heiko Carstens <heiko.carstens@de.ibm.com>
CC: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       "David S. Miller" <davem@davemloft.net>,
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       Andi Kleen <ak@muc.de>, Andrew Morton <akpm@osdl.org>,
       Linus Torvalds <torvalds@osdl.org>
Subject: Re: [PATCH] percpu data: only iterate over possible CPUs
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Heiko Carstens a écrit :
>> tree 8c30052a0d7fadec37c785a42a71b28d0a9c5fcf
>> parent cef5076987dd545ac74f4efcf1c962be8eac34b0
>> author Eric Dumazet <dada1@cosmosbay.com> Sun, 05 Feb 2006 15:27:36 -0800
>> committer Linus Torvalds <torvalds@g5.osdl.org> Mon, 06 Feb 2006 03:06:51 -0800
>>
>> [PATCH] percpu data: only iterate over possible CPUs
>>
>> percpu_data blindly allocates bootmem memory to store NR_CPUS instances of
>> cpudata, instead of allocating memory only for possible cpus.
>>
>> As a preparation for changing that, we need to convert various 0 -> NR_CPUS
>> loops to use for_each_cpu().
>>
>> (The above only applies to users of asm-generic/percpu.h.  powerpc has gone it
>> alone and is presently only allocating memory for present CPUs, so it's
>> currently corrupting memory).
> 
> This patch is broken since it replaces several loops that iterate NR_CPUS
> times with for_each_cpu before cpu_possible_map is setup:

This patch assumes that cpu_possible_map is setup before setup_per_cpu_areas().

That sounds a reasonable assumption, but maybe not on your architecture ?

I dont think cpu_possible_map has to be filled at smp_prepare_cpus() time, but 
long before.

On i386/x86_64/ia64, this is done from setup_arch() called from start_kernel() 
just before setup_per_cpu_areas()

On powerpc it's done from setup_system(), called before start_kernel()

Eric