From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx203.postini.com [74.125.245.203]) by kanga.kvack.org (Postfix) with SMTP id 32B116B0068 for ; Mon, 13 Aug 2012 20:23:06 -0400 (EDT) From: Rusty Russell Subject: Re: [PATCH v7 2/4] virtio_balloon: introduce migration primitives to balloon pages In-Reply-To: <20120813084123.GF14081@redhat.com> References: <20120813084123.GF14081@redhat.com> Date: Tue, 14 Aug 2012 09:29:49 +0930 Message-ID: <87lihis5qi.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org List-ID: To: "Michael S. Tsirkin" , Rafael Aquini Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Rik van Riel , Mel Gorman , Andi Kleen , Andrew Morton , Konrad Rzeszutek Wilk , Minchan Kim On Mon, 13 Aug 2012 11:41:23 +0300, "Michael S. Tsirkin" wrote: > On Fri, Aug 10, 2012 at 02:55:15PM -0300, Rafael Aquini wrote: > > +/* > > + * Populate balloon_mapping->a_ops->freepage method to help compaction on > > + * re-inserting an isolated page into the balloon page list. > > + */ > > +void virtballoon_putbackpage(struct page *page) > > +{ > > + spin_lock(&pages_lock); > > + list_add(&page->lru, &vb_ptr->pages); > > + spin_unlock(&pages_lock); > > Could the following race trigger: > migration happens while module unloading is in progress, > module goes away between here and when the function > returns, then code for this function gets overwritten? > If yes we need locking external to module to prevent this. > Maybe add a spinlock to struct address_space? The balloon module cannot be unloaded until it has leaked all its pages, so I think this is safe: static void remove_common(struct virtio_balloon *vb) { /* There might be pages left in the balloon: free them. */ while (vb->num_pages) leak_balloon(vb, vb->num_pages); Cheers, Rusty. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org