linux-kernel - Re: [PATCH v3 7/8] mips: numa: make node_to_cpumask_map() NUMA_NO

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Date:   Sun, 15 Sep 2019 14:13:51 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Mike Rapoport <rppt@...ux.ibm.com>
CC:     <catalin.marinas@....com>, <will@...nel.org>, <mingo@...hat.com>,
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Subject: Re: [PATCH v3 7/8] mips: numa: make node_to_cpumask_map()
 NUMA_NO_NODE aware for mips

On 2019/9/15 13:49, Mike Rapoport wrote:
> Hi,
> 
> On Thu, Sep 12, 2019 at 06:15:33PM +0800, Yunsheng Lin wrote:
>> When passing the return value of dev_to_node() to cpumask_of_node()
>> without checking the node id if the node id is NUMA_NO_NODE, there is
>> global-out-of-bounds detected by KASAN.
>>
>> From the discussion [1], NUMA_NO_NODE really means no node affinity,
>> which also means all cpus should be usable. So the cpumask_of_node()
>> should always return all cpus online when user passes the node id
>> as NUMA_NO_NODE, just like similar semantic that page allocator handles
>> NUMA_NO_NODE.
>>
>> But we cannot really copy the page allocator logic. Simply because the
>> page allocator doesn't enforce the near node affinity. It just picks it
>> up as a preferred node but then it is free to fallback to any other numa
>> node. This is not the case here and node_to_cpumask_map will only restrict
>> to the particular node's cpus which would have really non deterministic
>> behavior depending on where the code is executed. So in fact we really
>> want to return cpu_online_mask for NUMA_NO_NODE.
>>
>> Since this arch was already NUMA_NO_NODE aware, this patch only changes
>> it to return cpu_online_mask and use NUMA_NO_NODE instead of "-1".
>>
>> [1] https://lore.kernel.org/patchwork/patch/1125789/
>> Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com>
>> Suggested-by: Michal Hocko <mhocko@...nel.org>
>> ---
>> V3: Change to only handle NUMA_NO_NODE, and return cpu_online_mask
>>     for NUMA_NO_NODE case, and change the commit log to better justify
>>     the change.
>> ---
>>  arch/mips/include/asm/mach-ip27/topology.h | 4 ++--
> 
> Nit: the subject says "mips:", but this patch only touches sgi-ip27 and
> loongson is updated as a separate patch. I don't see why both patches
> cannot be merged. Moreover, the whole set can be made as a single patch,
> IMHO.

Thanks for reviewing.

As this patchset touches a few files, which may has different maintainer.
I am not sure if a separate patch for different arch will make the merging
process easy, or a single patch will make the merging process easy?

It can be made as a single patch if a single patch will make the merging
process easy.

> 
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/mips/include/asm/mach-ip27/topology.h b/arch/mips/include/asm/mach-ip27/topology.h
>> index 965f079..04505e6 100644
>> --- a/arch/mips/include/asm/mach-ip27/topology.h
>> +++ b/arch/mips/include/asm/mach-ip27/topology.h
>> @@ -15,8 +15,8 @@ struct cpuinfo_ip27 {
>>  extern struct cpuinfo_ip27 sn_cpu_info[NR_CPUS];
>>  
>>  #define cpu_to_node(cpu)	(sn_cpu_info[(cpu)].p_nodeid)
>> -#define cpumask_of_node(node)	((node) == -1 ?				\
>> -				 cpu_all_mask :				\
>> +#define cpumask_of_node(node)	((node) == NUMA_NO_NODE ?		\
>> +				 cpu_online_mask :			\
>>  				 &hub_data(node)->h_cpus)
>>  struct pci_bus;
>>  extern int pcibus_to_node(struct pci_bus *);
>> -- 
>> 2.8.1
>>
>