[PATCH v6] numa: make node_to_cpumask_map() NUMA_NO_NODE aware

[Yunsheng Lin]

On 2019/9/22 6:38, Paul Burton wrote:
> Hi Yunsheng,
> 
> On Tue, Sep 17, 2019 at 08:48:54PM +0800, Yunsheng Lin wrote:
>> When passing the return value of dev_to_node() to cpumask_of_node()
>> without checking if the device's 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.
>>
>> Also there is a debugging version of node_to_cpumask_map() for x86 and
>> arm64, which is only used when CONFIG_DEBUG_PER_CPU_MAPS is defined, this
>> patch changes it to handle NUMA_NO_NODE as normal node_to_cpumask_map().
>>
>> [1] https://lore.kernel.org/patchwork/patch/1125789/
>> Signed-off-by: Yunsheng Lin <linyunsheng at huawei.com>
>> Suggested-by: Michal Hocko <mhocko at kernel.org>
>> Acked-by: Michal Hocko <mhocko at suse.com>
> 
> If you end up sending another revision then I think it would be worth
> replacing -1 with NUMA_NO_NODE in
> arch/mips/include/asm/mach-ip27/topology.h for consistency, but in any
> case:

Perhaps it is better to replace -1 with NUMA_NO_NODE along with cpu_all_mask
-> cpu_online_mask change if the cpu_all_mask -> cpu_online_mask change is
reasonable.

Anyway, will do that if there is another version needed.

> 
>     Acked-by: Paul Burton <paul.burton at mips.com> # MIPS bits

Thanks for that.

> 
> Thanks,
>     Paul
> 
>> ---
>> V6: Drop the cpu_all_mask -> cpu_online_mask change for it seems a
>>     little controversial, may need deeper investigation, and rebased
>>     on the latest linux-next.
>> V5: Drop unsigned "fix" change for x86/arm64, and change comment log
>>     according to Michal's comment.
>> V4: Have all these changes in a single patch.
>> 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.
>> V2: make the node id checking change to other arches too.
>> ---
>>  arch/arm64/include/asm/numa.h                    | 3 +++
>>  arch/arm64/mm/numa.c                             | 3 +++
>>  arch/mips/include/asm/mach-loongson64/topology.h | 4 +++-
>>  arch/s390/include/asm/topology.h                 | 3 +++
>>  arch/x86/include/asm/topology.h                  | 3 +++
>>  arch/x86/mm/numa.c                               | 3 +++
>>  6 files changed, 18 insertions(+), 1 deletion(-)
> 
> .
>