linux-kernel - Re: [PATCH] mm: don't rely on system state to detect hot-plug operations

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Message-ID: <23a9ab54-a7bf-5bc2-2a60-e8a1246ed537@linux.ibm.com>
Date:   Wed, 9 Sep 2020 11:32:43 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...e.com>
Cc:     akpm@...ux-foundation.org, Oscar Salvador <osalvador@...e.de>,
        rafael@...nel.org, nathanl@...ux.ibm.com, cheloha@...ux.ibm.com,
        stable@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: don't rely on system state to detect hot-plug
 operations

Le 09/09/2020 à 11:24, David Hildenbrand a écrit :
>>> I am not sure an enum is going to make the existing situation less
>>> messy. Sure we somehow have to distinguish boot init and runtime hotplug
>>> because they have different constrains. I am arguing that a) we should
>>> have a consistent way to check for those and b) we shouldn't blow up
>>> easily just because sysfs infrastructure has failed to initialize.
>>
>> For the point a, using the enum allows to know in register_mem_sect_under_node()
>> if the link operation is due to a hotplug operation or done at boot time.
>>
>> For the point b, one option would be ignore the link error in the case the link
>> is already existing, but that BUG_ON() had the benefit to highlight the root issue.
>>
> 
> WARN_ON_ONCE() would be preferred  - not crash the system but still
> highlight the issue.

Indeed, calling sysfs_create_link() instead of sysfs_create_link_nowarn() in 
register_mem_sect_under_node() and ignoring EEXIST returned value should do the job.

I'll do that in a separate patch.