linux-kernel - Re: [PATCH v2] memory-hotplug: add automatic onlining policy for the newly added memory

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Message-ID: <871t9xto5f.fsf@vitty.brq.redhat.com>
Date:	Mon, 04 Jan 2016 15:28:12 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	<linux-mm@...ck.org>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>,
	Jonathan Corbet <corbet@....net>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	Daniel Kiper <daniel.kiper@...cle.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Xishi Qiu <qiuxishi@...wei.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	"Igor Mammedov" <imammedo@...hat.com>, Kay Sievers <kay@...y.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH v2] memory-hotplug: add automatic onlining policy for the newly added memory

David Vrabel <david.vrabel@...rix.com> writes:

> On 22/12/15 16:32, Vitaly Kuznetsov wrote:
>> @@ -1292,6 +1304,11 @@ int __ref add_memory_resource(int nid, struct resource *res)
>>  	/* create new memmap entry */
>>  	firmware_map_add_hotplug(start, start + size, "System RAM");
>>  
>> +	/* online pages if requested */
>> +	if (online)
>> +		online_pages(start >> PAGE_SHIFT, size >> PAGE_SHIFT,
>> +			     MMOP_ONLINE_KEEP);
>
> This will cause the Xen balloon driver to deadlock because it calls
> add_memory_resource() with the balloon_mutex locked and the online page
> callback also locks the balloon_mutex.

Currently xen ballon driver always calls add_memory_resource() with
online=false so this won't happen.

-- 
  Vitaly
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