From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751983Ab3LQAbY (ORCPT ); Mon, 16 Dec 2013 19:31:24 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:47455 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750986Ab3LQAbX (ORCPT ); Mon, 16 Dec 2013 19:31:23 -0500 Date: Mon, 16 Dec 2013 16:31:20 -0800 From: Andrew Morton To: Vlastimil Babka Cc: Sasha Levin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman , Rik van Riel , joern@logfs.org, Michel Lespinasse , stable@kernel.org Subject: Re: [PATCH 2/3] mm: munlock: fix deadlock in __munlock_pagevec() Message-Id: <20131216163120.28218456e2c870c4c1bfce1e@linux-foundation.org> In-Reply-To: <1387188856-21027-3-git-send-email-vbabka@suse.cz> References: <52AE07B4.4020203@oracle.com> <1387188856-21027-1-git-send-email-vbabka@suse.cz> <1387188856-21027-3-git-send-email-vbabka@suse.cz> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 16 Dec 2013 11:14:15 +0100 Vlastimil Babka wrote: > Commit 7225522bb ("mm: munlock: batch non-THP page isolation and > munlock+putback using pagevec" introduced __munlock_pagevec() to speed up > munlock by holding lru_lock over multiple isolated pages. Pages that fail to > be isolated are put_back() immediately, also within the lock. > > This can lead to deadlock when __munlock_pagevec() becomes the holder of the > last page pin and put_back() leads to __page_cache_release() which also locks > lru_lock. The deadlock has been observed by Sasha Levin using trinity. > > This patch avoids the deadlock by deferring put_back() operations until > lru_lock is released. Another pagevec (which is also used by later phases > of the function is reused to gather the pages for put_back() operation. > > ... > Thanks for fixing this one. I'll cross it off the rather large list of recent MM regressions :( > --- a/mm/mlock.c > +++ b/mm/mlock.c > @@ -295,10 +295,12 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone) > { > int i; > int nr = pagevec_count(pvec); > - int delta_munlocked = -nr; > + int delta_munlocked; > struct pagevec pvec_putback; > int pgrescued = 0; > > + pagevec_init(&pvec_putback, 0); > + > /* Phase 1: page isolation */ > spin_lock_irq(&zone->lru_lock); > for (i = 0; i < nr; i++) { > @@ -327,16 +329,22 @@ skip_munlock: > /* > * We won't be munlocking this page in the next phase > * but we still need to release the follow_page_mask() > - * pin. > + * pin. We cannot do it under lru_lock however. If it's > + * the last pin, __page_cache_release would deadlock. > */ > + pagevec_add(&pvec_putback, pvec->pages[i]); > pvec->pages[i] = NULL; > - put_page(page); > - delta_munlocked++; > } > } > + delta_munlocked = -nr + pagevec_count(&pvec_putback); > __mod_zone_page_state(zone, NR_MLOCK, delta_munlocked); > spin_unlock_irq(&zone->lru_lock); > > + /* Now we can release pins of pages that we are not munlocking */ > + for (i = 0; i < pagevec_count(&pvec_putback); i++) { > + put_page(pvec_putback.pages[i]); > + } > + We could just do --- a/mm/mlock.c~mm-munlock-fix-deadlock-in-__munlock_pagevec-fix +++ a/mm/mlock.c @@ -341,12 +341,9 @@ skip_munlock: spin_unlock_irq(&zone->lru_lock); /* Now we can release pins of pages that we are not munlocking */ - for (i = 0; i < pagevec_count(&pvec_putback); i++) { - put_page(pvec_putback.pages[i]); - } + pagevec_release(&pvec_putback); /* Phase 2: page munlock */ - pagevec_init(&pvec_putback, 0); for (i = 0; i < nr; i++) { struct page *page = pvec->pages[i]; The lru_add_drain() is unnecessary overhead here. What do you think?