linux-kernel - Re: [PATCH 1/4] mmzone: make holding lock_memory_hotplug() a requirement for updating pgdat size

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Message-ID: <518197E2.7050004@linux.vnet.ibm.com>
Date:	Wed, 01 May 2013 15:32:02 -0700
From:	Cody P Schafer <cody@...ux.vnet.ibm.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] mmzone: make holding lock_memory_hotplug() a requirement
 for updating pgdat size

On 05/01/2013 03:26 PM, David Rientjes wrote:
> On Wed, 1 May 2013, Cody P Schafer wrote:
>
>> All updaters of pgdat size (spanned_pages, start_pfn, and
>> present_pages) currently also hold lock_memory_hotplug() (in addition
>> to pgdat_resize_lock()).
>>
>> Document this and make holding of that lock a requirement on the update
>> side for now, but keep the pgdat_resize_lock() around for readers that
>> can't lock a mutex.
>>
>> Signed-off-by: Cody P Schafer <cody@...ux.vnet.ibm.com>
>
> Nack, these fields are initialized at boot without lock_memory_hotplug(),
> so you're statement is wrong, and all you need is pgdat_resize_lock().

They are also initialized at boot without pgdat_resize_lock(), if we 
consider boot time, quite a few of the statements on when locking is 
required are wrong.

That said, you are correct that it is not strictly required to hold 
lock_memory_hotplug() when updating the fields in question because 
pgdat_resize_lock() is used.



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