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Message-ID: <568A560A.80906@citrix.com>
Date: Mon, 4 Jan 2016 11:22:50 +0000
From: David Vrabel <david.vrabel@citrix.com>
MIME-Version: 1.0
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>
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Sender: owner-linux-mm@kvack.org
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To: Vitaly Kuznetsov <vkuznets@redhat.com>, linux-mm@kvack.org
Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, Jonathan Corbet <corbet@lwn.net>, Greg
 Kroah-Hartman <gregkh@linuxfoundation.org>, Daniel Kiper <daniel.kiper@oracle.com>, Dan Williams <dan.j.williams@intel.com>, Tang Chen <tangchen@cn.fujitsu.com>, David Rientjes <rientjes@google.com>, Andrew
 Morton <akpm@linux-foundation.org>, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, Xishi Qiu <qiuxishi@huawei.com>, Mel Gorman <mgorman@techsingularity.net>, "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>

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.

David

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