From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CCF5BC76191 for ; Thu, 18 Jul 2019 04:31:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A6B5F2077C for ; Thu, 18 Jul 2019 04:31:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727673AbfGREbq (ORCPT ); Thu, 18 Jul 2019 00:31:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37912 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725976AbfGREbq (ORCPT ); Thu, 18 Jul 2019 00:31:46 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 73314308FBA9; Thu, 18 Jul 2019 04:31:45 +0000 (UTC) Received: from redhat.com (ovpn-120-147.rdu2.redhat.com [10.10.120.147]) by smtp.corp.redhat.com (Postfix) with SMTP id 87DBA5D71D; Thu, 18 Jul 2019 04:31:33 +0000 (UTC) Date: Thu, 18 Jul 2019 00:31:31 -0400 From: "Michael S. Tsirkin" To: Wei Wang Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, xdeguillard@vmware.com, namit@vmware.com, akpm@linux-foundation.org, pagupta@redhat.com, riel@surriel.com, dave.hansen@intel.com, david@redhat.com, konrad.wilk@oracle.com, yang.zhang.wz@gmail.com, nitesh@redhat.com, lcapitulino@redhat.com, aarcange@redhat.com, pbonzini@redhat.com, alexander.h.duyck@linux.intel.com, dan.j.williams@intel.com Subject: Re: [PATCH v1] mm/balloon_compaction: avoid duplicate page removal Message-ID: <20190718001605-mutt-send-email-mst@kernel.org> References: <1563416610-11045-1-git-send-email-wei.w.wang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1563416610-11045-1-git-send-email-wei.w.wang@intel.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.43]); Thu, 18 Jul 2019 04:31:45 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 18, 2019 at 10:23:30AM +0800, Wei Wang wrote: > Fixes: 418a3ab1e778 (mm/balloon_compaction: List interfaces) > > A #GP is reported in the guest when requesting balloon inflation via > virtio-balloon. The reason is that the virtio-balloon driver has > removed the page from its internal page list (via balloon_page_pop), > but balloon_page_enqueue_one also calls "list_del" to do the removal. I would add here "this is necessary when it's used from balloon_page_enqueue_list but not when it's called from balloon_page_enqueue". > So remove the list_del in balloon_page_enqueue_one, and have the callers > do the page removal from their own page lists. > > Signed-off-by: Wei Wang Patch is good but comments need some work. > --- > mm/balloon_compaction.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c > index 83a7b61..1a5ddc4 100644 > --- a/mm/balloon_compaction.c > +++ b/mm/balloon_compaction.c > @@ -11,6 +11,7 @@ > #include > #include > > +/* Callers ensure that @page has been removed from its original list. */ This comment does not make sense. E.g. balloon_page_enqueue does nothing to ensure this. And drivers are not supposed to care how the page lists are managed. Pls drop. Instead please add the following to balloon_page_enqueue: Note: drivers must not call balloon_page_list_enqueue on pages that have been pushed to a list with balloon_page_push before removing them with balloon_page_pop. To all pages on a list, use balloon_page_list_enqueue instead. > static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info, > struct page *page) > { > @@ -21,7 +22,6 @@ static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info, > * memory corruption is possible and we should stop execution. > */ > BUG_ON(!trylock_page(page)); > - list_del(&page->lru); > balloon_page_insert(b_dev_info, page); > unlock_page(page); > __count_vm_event(BALLOON_INFLATE); > @@ -47,6 +47,7 @@ size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info, > > spin_lock_irqsave(&b_dev_info->pages_lock, flags); > list_for_each_entry_safe(page, tmp, pages, lru) { > + list_del(&page->lru); > balloon_page_enqueue_one(b_dev_info, page); > n_pages++; > } > -- > 2.7.4