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Date:   Mon, 31 Jan 2022 08:48:54 +0100
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Subject: Re: [PATCH RFC v1] drivers/base/node: consolidate node device
 subsystem initialization in node_dev_init()
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To:     Oscar Salvador <osalvador@suse.de>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Michal Hocko <mhocko@suse.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>,
        "David S. Miller" <davem@davemloft.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>, x86@kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org,
        linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
        linux-sh@vger.kernel.org, sparclinux@vger.kernel.org
References: <20220128151540.164759-1-david@redhat.com>
 <YfeARpenqPii1WQH@localhost.localdomain>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
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On 31.01.22 07:23, Oscar Salvador wrote:
> On Fri, Jan 28, 2022 at 04:15:40PM +0100, David Hildenbrand wrote:
>> ... and call node_dev_init() after memory_dev_init() from driver_init(),
>> so before any of the existing arch/subsys calls. All online nodes should
>> be known at that point.
>>
>> This is in line with memory_dev_init(), which initializes the memory
>> device subsystem and creates all memory block devices.
>>
>> Similar to memory_dev_init(), panic() if anything goes wrong, we don't
>> want to continue with such basic initialization errors.
>>
>> The important part is that node_dev_init() gets called after
>> memory_dev_init() and after cpu_dev_init(), but before any of the
>> relevant archs call register_cpu() to register the new cpu device under
>> the node device. The latter should be the case for the current users
>> of topology_init().
> 

Hi Oscar,

> So, before this change we had something like this:
> 
> do_basic_setup
>  driver_init
>   memory_dev_init
>  do_init_calls
>   ...
>    topology_init
>     register_nodes/register_one_node
> 
> And after the patch all happens in driver_init()
> 
> driver_init
>  memory_dev_init
>  node_dev_init
> 
> I guess this is fine as we do not have any ordering problems (aka: none
> of the functions we used to call before expect the nodes not to be
> there for some weird reason).
> 
> So, no functional change, right?
> 

Right, and the idea is that the online state of nodes (+ node/zone
ranges) already has to be known at that point in time, because
otherwise, we'd be in bigger trouble.

Thanks!


-- 
Thanks,

David / dhildenb