linux-kernel - Re: [linux41] regression with 'x86/cacheinfo: Move cacheinfo sysfs code to generic infrastructure' on AMD i686

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Date:	Sun, 26 Jul 2015 12:54:55 +0200
From:	Philip Müller <philm@...jaro.org>
To:	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>,
	Guenter Roeck <linux@...ck-us.net>, manjaro-dev@...jaro.org,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andre Przywara <andre.przywara@....com>,
	Borislav Petkov <bp@...e.de>
Subject: Re: [linux41] regression with 'x86/cacheinfo: Move cacheinfo sysfs
 code to generic infrastructure' on AMD i686

Hi Borislav,

I can confirm your patch working. However, it might be good to use yours
and Thomas' in combination to solve this properly.

kind regards
Philip

On 26.07.2015 10:41, Borislav Petkov wrote:
> On Sun, Jul 26, 2015 at 10:13:45AM +0200, Thomas Gleixner wrote:
>> On Sun, 26 Jul 2015, Philip Müller wrote:
>>>> task: f58e0000 ti: f58e8000 task.ti: f58e800
>>>> EIP: 0060:[<c135a903>] EFLAGS: 00010206 CPU: 0
>>>> EIP is at free_cache_attributes+0x83/0xd0
>>>> EAX: 00000001 EBX: f589d46c ECX: 00000090 EDX: 360c2000
>>>> ESI: 00000000 EDI: c1724a80 EBP: f58e9ec0 ESP: f58e9ea0
>>>>  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
>>>> CR0: 8005003b CR2: 000000ac CR3: 01731000 CR4: 000006d0
>>
>> That's a trivial NULL pointer dereference in the error/cleanup
>> path. Patch below should fix it.
> 
> Well, I got a bit different, and of course totally untested possible
> solution:
> 
> cache_shared_cpu_map_setup() does check sib_cpu_ci->info_list before
> setting cpumask bits while cache_shared_cpu_map_remove() doesn't. Ballancing
> this out would mean:
> 
> ---
> diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
> index 764280a91776..8a4546dc25e3 100644
> --- a/drivers/base/cacheinfo.c
> +++ b/drivers/base/cacheinfo.c
> @@ -148,7 +148,11 @@ static void cache_shared_cpu_map_remove(unsigned int cpu)
>  
>  			if (sibling == cpu) /* skip itself */
>  				continue;
> +
>  			sib_cpu_ci = get_cpu_cacheinfo(sibling);
> +			if (!sib_cpu_ci->info_list)
> +				continue;
> +
>  			sib_leaf = sib_cpu_ci->info_list + index;
>  			cpumask_clear_cpu(cpu, &sib_leaf->shared_cpu_map);
>  			cpumask_clear_cpu(sibling, &this_leaf->shared_cpu_map);
> ---
> 
> Now Philip can have some more fun testing :-)
> 

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