linux-kernel - Re: [PATCH] powerpc/64e: drop stale call to smp_processor

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Date:   Thu, 8 Aug 2019 21:12:11 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     "christophe.leroy@....fr" <christophe.leroy@....fr>,
        "paulus@...ba.org" <paulus@...ba.org>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>
CC:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powerpc/64e: drop stale call to smp_processor_id() which
 hangs SMP startup

Hi Christophe,

On Thu, 2019-08-08 at 12:48 +0000, Christophe Leroy wrote:
> Santa commit ebb9d30a6a74 ("powerpc/mm: any thread in one core can be
> the first to setup TLB1") removed the need to know the cpu_id in
> early_init_this_mmu(), but the call to smp_processor_id() which was
> marked __maybe_used remained.
> 
> Since commit ed1cd6deb013 ("powerpc: Activate
> CONFIG_THREAD_INFO_IN_TASK") thread_info cannot be reached before mmu
> is properly set up.
> 
> Drop this stale call to smp_processor_id() which make SMP hang
> when CONFIG_PREEMPT is set.
> 
> Reported-by: Chris Packham <Chris.Packham@...iedtelesis.co.nz>
> Fixes: ebb9d30a6a74 ("powerpc/mm: any thread in one core can be the
> first to setup TLB1")
> Link: https://github.com/linuxppc/issues/issues/264
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> Cc: stable@...r.kernel.org

Many thanks for your help.

Tested-by: Chris Packham <chris.packham@...iedtelesis.co.nz>

> ---
>  arch/powerpc/mm/nohash/tlb.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/powerpc/mm/nohash/tlb.c
> b/arch/powerpc/mm/nohash/tlb.c
> index d4acf6fa0596..bf60983a58c7 100644
> --- a/arch/powerpc/mm/nohash/tlb.c
> +++ b/arch/powerpc/mm/nohash/tlb.c
> @@ -630,7 +630,6 @@ static void early_init_this_mmu(void)
>  #ifdef CONFIG_PPC_FSL_BOOK3E
>  	if (mmu_has_feature(MMU_FTR_TYPE_FSL_E)) {
>  		unsigned int num_cams;
> -		int __maybe_unused cpu = smp_processor_id();
>  		bool map = true;
>  
>  		/* use a quarter of the TLBCAM for bolted linear map
> */