From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754163AbbE1OB3 (ORCPT ); Thu, 28 May 2015 10:01:29 -0400 Received: from cantor2.suse.de ([195.135.220.15]:52173 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752769AbbE1OBW (ORCPT ); Thu, 28 May 2015 10:01:22 -0400 Message-ID: <1432821670.13915.3.camel@stgolabs.net> Subject: Re: [PATCH v3 3/3] mm/hugetlb: handle races in alloc_huge_page and hugetlb_reserve_pages From: Davidlohr Bueso To: Mike Kravetz Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Naoya Horiguchi , David Rientjes , Luiz Capitulino , Andrew Morton Date: Thu, 28 May 2015 07:01:10 -0700 In-Reply-To: <1432749371-32220-4-git-send-email-mike.kravetz@oracle.com> References: <1432749371-32220-1-git-send-email-mike.kravetz@oracle.com> <1432749371-32220-4-git-send-email-mike.kravetz@oracle.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.11 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2015-05-27 at 10:56 -0700, Mike Kravetz wrote: > alloc_huge_page and hugetlb_reserve_pages use region_chg to > calculate the number of pages which will be added to the reserve > map. Subpool and global reserve counts are adjusted based on > the output of region_chg. Before the pages are actually added > to the reserve map, these routines could race and add fewer > pages than expected. If this happens, the subpool and global > reserve counts are not correct. > > Compare the number of pages actually added (region_add) to those > expected to added (region_chg). If fewer pages are actually added, > this indicates a race and adjust counters accordingly. > > Signed-off-by: Mike Kravetz Reviewed-by: Davidlohr Bueso With one nit below. > --- > mm/hugetlb.c | 34 ++++++++++++++++++++++++++++++---- > 1 file changed, 30 insertions(+), 4 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index b3d3d59..038c84e 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -1544,7 +1544,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma, > struct hugepage_subpool *spool = subpool_vma(vma); > struct hstate *h = hstate_vma(vma); > struct page *page; > - long chg; > + long chg, commit; > int ret, idx; > struct hugetlb_cgroup *h_cg; > > @@ -1585,7 +1585,20 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma, > > set_page_private(page, (unsigned long)spool); > > - vma_commit_reservation(h, vma, addr); > + commit = vma_commit_reservation(h, vma, addr); > + if (unlikely(chg > commit)) { > + /* > + * The page was added to the reservation map between > + * vma_needs_reservation and vma_commit_reservation. > + * This indicates a race with hugetlb_reserve_pages. > + * Adjust for the subpool count incremented above AND > + * in hugetlb_reserve_pages for the same page. Also, > + * the reservation count added in hugetlb_reserve_pages > + * no longer applies. > + */ > + hugepage_subpool_put_pages(spool, 1); > + hugetlb_acct_memory(h, -1); Should these fixups be encapsulated in a helper? The comment is the same for both alloc_huge_page and hugetlb_reserve_pages. Thanks, Davidlohr > + } > return page; > > out_uncharge_cgroup: > @@ -3699,8 +3712,21 @@ int hugetlb_reserve_pages(struct inode *inode, > * consumed reservations are stored in the map. Hence, nothing > * else has to be done for private mappings here > */ > - if (!vma || vma->vm_flags & VM_MAYSHARE) > - region_add(resv_map, from, to); > + if (!vma || vma->vm_flags & VM_MAYSHARE) { > + long add = region_add(resv_map, from, to); > + > + if (unlikely(chg > add)) { > + /* > + * pages in this range were added to the reserve > + * map between region_chg and region_add. This > + * indicates a race with alloc_huge_page. Adjust > + * the subpool and reserve counts modified above > + * based on the difference. > + */ > + hugepage_subpool_put_pages(spool, chg - add); > + hugetlb_acct_memory(h, -(chg - ret)); > + } > + } > return 0; > out_err: > if (vma && is_vma_resv_set(vma, HPAGE_RESV_OWNER))