linux-kernel - Re: [PATCH] mm,memory_hotplug: Drop unneeded locking

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Date:   Tue, 1 Jun 2021 10:02:54 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>,
        Anshuman Khandual <anshuman.khandual@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Pavel Tatashin <pasha.tatashin@...een.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm,memory_hotplug: Drop unneeded locking

On 01.06.21 09:47, Oscar Salvador wrote:
> On Tue, Jun 01, 2021 at 10:47:31AM +0530, Anshuman Khandual wrote:
>> Should also just drop zone_span_write[lock|unlock]() helpers as there
>> are no users left ?
> 
> Yes, definitely.
> Andrew, can you squash this on top? Thanks:
> 
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index a7fd2c3ccb77..27d8ba1d32cb 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -67,10 +67,6 @@ struct range mhp_get_pluggable_range(bool need_mapping);
>   
>   /*
>    * Zone resizing functions
> - *
> - * Note: any attempt to resize a zone should has pgdat_resize_lock()
> - * zone_span_writelock() both held. This ensure the size of a zone
> - * can't be changed while pgdat_resize_lock() held.
>    */
>   static inline unsigned zone_span_seqbegin(struct zone *zone)
>   {
> @@ -80,14 +76,6 @@ static inline int zone_span_seqretry(struct zone *zone, unsigned iv)
>   {
>   	return read_seqretry(&zone->span_seqlock, iv);
>   }
> -static inline void zone_span_writelock(struct zone *zone)
> -{
> -	write_seqlock(&zone->span_seqlock);
> -}
> -static inline void zone_span_writeunlock(struct zone *zone)
> -{
> -	write_sequnlock(&zone->span_seqlock);
> -}

If there is no writer anymore, why do we have to protect readers?



-- 
Thanks,

David / dhildenb