linux-kernel - Re: [PATCH RFC v1] drivers/base/node: consolidate node device subsystem initialization in node_dev

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Message-ID: <3be2e20c-f0b9-c080-adf4-b0e17c046eb0@redhat.com>
Date:   Mon, 31 Jan 2022 08:48:54 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH RFC v1] drivers/base/node: consolidate node device
 subsystem initialization in node_dev_init()

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