linux-kernel - Re: [PATCH v2 RESEND 1/2] arm, arm64: change_memory_common with numpages == 0 should be no-op.

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Date:	Tue, 26 Jan 2016 15:14:11 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Will Deacon <will.deacon@....com>
cc:	mika.penttila@...tfour.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux@....linux.org.uk, catalin.marinas@....com
Subject: Re: [PATCH v2 RESEND 1/2] arm, arm64: change_memory_common with
 numpages == 0 should be no-op.

On Tue, 26 Jan 2016, Will Deacon wrote:

> From 57adec866c0440976c96a4b8f5b59fb411b1cacb Mon Sep 17 00:00:00 2001
> From: =?UTF-8?q?Mika=20Penttil=C3=A4?= <mika.penttila@...tfour.com>
> Date: Tue, 26 Jan 2016 15:47:25 +0000
> Subject: [PATCH] arm64: mm: avoid calling apply_to_page_range on empty range
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
> 
> Calling apply_to_page_range with an empty range results in a BUG_ON
> from the core code. This can be triggered by trying to load the st_drv
> module with CONFIG_DEBUG_SET_MODULE_RONX enabled:
> 
>   kernel BUG at mm/memory.c:1874!
>   Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
>   Modules linked in:
>   CPU: 3 PID: 1764 Comm: insmod Not tainted 4.5.0-rc1+ #2
>   Hardware name: ARM Juno development board (r0) (DT)
>   task: ffffffc9763b8000 ti: ffffffc975af8000 task.ti: ffffffc975af8000
>   PC is at apply_to_page_range+0x2cc/0x2d0
>   LR is at change_memory_common+0x80/0x108
> 
> This patch fixes the issue by making change_memory_common (called by the
> set_memory_* functions) a NOP when numpages == 0, therefore avoiding the
> erroneous call to apply_to_page_range and bringing us into line with x86
> and s390.
> 
> Cc: <stable@...r.kernel.org>
> Reviewed-by: Laura Abbott <labbott@...hat.com>
> Acked-by: David Rientjes <rientjes@...gle.com>
> Signed-off-by: Mika Penttilä <mika.penttila@...tfour.com>
> Signed-off-by: Will Deacon <will.deacon@....com>
> ---
>  arch/arm64/mm/pageattr.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index 3571c7309c5e..cf6240741134 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -57,6 +57,9 @@ static int change_memory_common(unsigned long addr, int numpages,
>  	if (end < MODULES_VADDR || end >= MODULES_END)
>  		return -EINVAL;
>  
> +	if (!numpages)
> +		return 0;
> +
>  	data.set_mask = set_mask;
>  	data.clear_mask = clear_mask;
>  

LGTM, I think this issue goes back to 3.17 due to commit 11d91a770f1f 
("arm64: Add CONFIG_DEBUG_SET_MODULE_RONX support") so perhaps annotate 
the stable@...r.kernel.org for 3.17+.