linux-kernel - Re: [PATCH v2] mm: BUG when __kmap_atomic_idx equals KM_TYPE

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Message-ID: <alpine.DEB.2.02.1407310001360.18238@chino.kir.corp.google.com>
Date:	Thu, 31 Jul 2014 00:02:38 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Chintan Pandya <cpandya@...eaurora.org>
cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH v2] mm: BUG when __kmap_atomic_idx equals KM_TYPE_NR

On Thu, 31 Jul 2014, Chintan Pandya wrote:

> __kmap_atomic_idx is per_cpu variable. Each CPU can
> use KM_TYPE_NR entries from FIXMAP i.e. from 0 to
> KM_TYPE_NR - 1. Allowing __kmap_atomic_idx to over-
> shoot to KM_TYPE_NR can mess up with next CPU's 0th
> entry which is a bug. Hence BUG_ON if
> __kmap_atomic_idx >= KM_TYPE_NR.
> 

This appears to be a completely different patch, not a v2.  Why is this 
check only done for CONFIG_DEBUG_HIGHMEM?

I think Andrew's comment earlier was referring to the changelog only and 
not the patch, which looked correct.

> Signed-off-by: Chintan Pandya <cpandya@...eaurora.org>
> ---
> Changes:
> 
> V1 --> V2
> 
> 	Not touching CONFIG_DEBUG_HIGHMEM.
> 
>  include/linux/highmem.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index 7fb31da..9286a46 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -93,7 +93,7 @@ static inline int kmap_atomic_idx_push(void)
>  
>  #ifdef CONFIG_DEBUG_HIGHMEM
>  	WARN_ON_ONCE(in_irq() && !irqs_disabled());
> -	BUG_ON(idx > KM_TYPE_NR);
> +	BUG_ON(idx >= KM_TYPE_NR);
>  #endif
>  	return idx;
>  }
--
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