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

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Message-Id: <20190915054901.GC11429@linux.ibm.com>
Date:   Sun, 15 Sep 2019 08:49:02 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Yunsheng Lin <linyunsheng@...wei.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

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.

>  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
> 

-- 
Sincerely yours,
Mike.