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From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: David Vrabel <david.vrabel@citrix.com>
Cc: <linux-mm@kvack.org>, <linux-doc@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <xen-devel@lists.xenproject.org>,
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        "K. Y. Srinivasan" <kys@microsoft.com>,
        "Igor Mammedov" <imammedo@redhat.com>, Kay Sievers <kay@vrfy.org>,
        "Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH v2] memory-hotplug: add automatic onlining policy for the newly added memory
References: <1450801950-7744-1-git-send-email-vkuznets@redhat.com>
	<568A560A.80906@citrix.com>
Date: Mon, 04 Jan 2016 15:28:12 +0100
In-Reply-To: <568A560A.80906@citrix.com> (David Vrabel's message of "Mon, 4
	Jan 2016 11:22:50 +0000")
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David Vrabel <david.vrabel@citrix.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