linux-kernel - Re: [PATCH v2] MIPS: PCI: Fix smp_processor

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Date:   Tue, 25 Jul 2017 08:39:29 -0400
From:   Joshua Kinard <kumba@...too.org>
To:     Matt Redfearn <matt.redfearn@...tec.com>,
        Ralf Baechle A <ralf@...ux-mips.org>
Cc:     linux-mips@...ux-mips.org, "Maciej W. Rozycki" <macro@...tec.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-kernel@...r.kernel.org, James Hogan <james.hogan@...tec.com>,
        Paul Burton <paul.burton@...tec.com>
Subject: Re: [PATCH v2] MIPS: PCI: Fix smp_processor_id() in preemptible

On 07/25/2017 05:39, Matt Redfearn wrote:
> Commit 1c3c5eab1715 ("sched/core: Enable might_sleep() and
> smp_processor_id() checks early") enables checks for might_sleep() and
> smp_processor_id() being used in preemptible code earlier in the boot
> than before. This results in a new BUG from
> pcibios_set_cache_line_size().
> 
> BUG: using smp_processor_id() in preemptible [00000000] code:
> swapper/0/1
> caller is pcibios_set_cache_line_size+0x10/0x70
> CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.13.0-rc1-00007-g3ce3e4ba4275 #615
> Stack : 0000000000000000 ffffffff81189694 0000000000000000 ffffffff81822318
>         000000000000004e 0000000000000001 800000000e20bd08 20c49ba5e3540000
>         0000000000000000 0000000000000000 ffffffff818d0000 0000000000000000
>         0000000000000000 ffffffff81189328 ffffffff818ce692 0000000000000000
>         0000000000000000 ffffffff81189bc8 ffffffff818d0000 0000000000000000
>         ffffffff81828907 ffffffff81769970 800000020ec78d80 ffffffff818c7b48
>         0000000000000001 0000000000000001 ffffffff818652b0 ffffffff81896268
>         ffffffff818c0000 800000020ec7fb40 800000020ec7fc58 ffffffff81684cac
>         0000000000000000 ffffffff8118ab50 0000000000000030 ffffffff81769970
>         0000000000000001 ffffffff81122a58 0000000000000000 0000000000000000
>         ...
> Call Trace:
> [<ffffffff81122a58>] show_stack+0x90/0xb0
> [<ffffffff81684cac>] dump_stack+0xac/0xf0
> [<ffffffff813f7050>] check_preemption_disabled+0x120/0x128
> [<ffffffff818855e8>] pcibios_set_cache_line_size+0x10/0x70
> [<ffffffff81100578>] do_one_initcall+0x48/0x140
> [<ffffffff81865dc4>] kernel_init_freeable+0x194/0x24c
> [<ffffffff8169c534>] kernel_init+0x14/0x118
> [<ffffffff8111ca84>] ret_from_kernel_thread+0x14/0x1c
> 
> Fix this by using the cpu_*cache_line_size() macros instead. These
> macros are the "proper" way to determine the CPU cache sizes.
> Since no cpu_tcache_line_size exists yet, add it.
> 
> Fixes: 1c3c5eab1715 ("sched/core: Enable might_sleep() and smp_processor_id() checks early")
> Signed-off-by: Matt Redfearn <matt.redfearn@...tec.com>
> Suggested-by: James Hogan <james.hogan@...tec.com>
> Reviewed-by: James Hogan <james.hogan@...tec.com>
> ---
> 
> Changes in v2:
> Switch to using cpu_*cache_line_size() macros
> 
> In heteregenerous systems the more correct fix for this would be to
> iterate over CPUs checking each ones cache hierarchy. However, as no
> such systems currently exist that seems wasteful.
> 
> ---
>  arch/mips/include/asm/cpu-features.h | 3 +++
>  arch/mips/pci/pci.c                  | 7 +++----
>  2 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/mips/include/asm/cpu-features.h b/arch/mips/include/asm/cpu-features.h
> index 8baa9033b181..721b698bfe3c 100644
> --- a/arch/mips/include/asm/cpu-features.h
> +++ b/arch/mips/include/asm/cpu-features.h
> @@ -428,6 +428,9 @@
>  #ifndef cpu_scache_line_size
>  #define cpu_scache_line_size()	cpu_data[0].scache.linesz
>  #endif
> +#ifndef cpu_tcache_line_size
> +#define cpu_tcache_line_size()	cpu_data[0].tcache.linesz
> +#endif
>  
>  #ifndef cpu_hwrena_impl_bits
>  #define cpu_hwrena_impl_bits		0

Not to be pedantic, but shouldn't the addition of an unimplemented
function/macro be a separate patch and this change become a (small) patch series?


> diff --git a/arch/mips/pci/pci.c b/arch/mips/pci/pci.c
> index bd67ac74fe2d..9632436d74d7 100644
> --- a/arch/mips/pci/pci.c
> +++ b/arch/mips/pci/pci.c
> @@ -28,16 +28,15 @@ EXPORT_SYMBOL(PCIBIOS_MIN_MEM);
>  
>  static int __init pcibios_set_cache_line_size(void)
>  {
> -	struct cpuinfo_mips *c = &current_cpu_data;
>  	unsigned int lsize;
>  
>  	/*
>  	 * Set PCI cacheline size to that of the highest level in the
>  	 * cache hierarchy.
>  	 */
> -	lsize = c->dcache.linesz;
> -	lsize = c->scache.linesz ? : lsize;
> -	lsize = c->tcache.linesz ? : lsize;
> +	lsize = cpu_dcache_line_size();
> +	lsize = cpu_scache_line_size() ? : lsize;
> +	lsize = cpu_tcache_line_size() ? : lsize;
>  
>  	BUG_ON(!lsize);


-- 
Joshua Kinard
Gentoo/MIPS
kumba@...too.org
6144R/F5C6C943 2015-04-27
177C 1972 1FB8 F254 BAD0 3E72 5C63 F4E3 F5C6 C943

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