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:	Wed, 27 Jan 2016 18:04:38 +0200
From:	Mika Penttilä <mika.penttila@...tfour.com>
To:	Will Deacon <will.deacon@....com>
CC:	<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.


Hi Will,

On 26.01.2016 17:59, Will Deacon wrote:
> Hi Mika,
>
> On Tue, Jan 26, 2016 at 04:59:52PM +0200, mika.penttila@...tfour.com wrote:
>> From: Mika Penttilä <mika.penttila@...tfour.com>
>>
>> This makes the caller set_memory_xx() consistent with x86.
>>
>> arm64 part is rebased on 4.5.0-rc1 with Ard's patch
>>  lkml.kernel.org/g/<1453125665-26627-1-git-send-email-ard.biesheuvel@...aro.org>
>> applied.
>>
>> Signed-off-by: Mika Penttilä mika.penttila@...tfour.com
>> Reviewed-by: Laura Abbott <labbott@...hat.com>
>> Acked-by: David Rientjes <rientjes@...gle.com>
>>
>> ---
>>  arch/arm/mm/pageattr.c   | 3 +++
>>  arch/arm64/mm/pageattr.c | 3 +++
>>  2 files changed, 6 insertions(+)
>>
>> diff --git a/arch/arm/mm/pageattr.c b/arch/arm/mm/pageattr.c
>> index cf30daf..d19b1ad 100644
>> --- a/arch/arm/mm/pageattr.c
>> +++ b/arch/arm/mm/pageattr.c
>> @@ -49,6 +49,9 @@ static int change_memory_common(unsigned long addr, int numpages,
>>  		WARN_ON_ONCE(1);
>>  	}
>>  
>> +	if (!numpages)
>> +		return 0;
>> +
>>  	if (start < MODULES_VADDR || start >= MODULES_END)
>>  		return -EINVAL;
>>  
>> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
>> index 1360a02..b582fc2 100644
>> --- a/arch/arm64/mm/pageattr.c
>> +++ b/arch/arm64/mm/pageattr.c
>> @@ -53,6 +53,9 @@ static int change_memory_common(unsigned long addr, int numpages,
>>  		WARN_ON_ONCE(1);
>>  	}
>>  
>> +	if (!numpages)
>> +		return 0;
>> +
> Thanks for this. I can reproduce the failure on my Juno board, so I'd
> like to queue this for 4.5 since it fixes a real issue. I've taken the
> liberty of rebasing the arm64 part to my fixes branch and writing a
> commit message. Does the patch below look ok to you?
>
> Will
>
> --->8
>
> 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;
>  

Yes I'm fine with that,
Thanks!
Mika