From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id D84286B0003 for ; Thu, 15 Mar 2018 14:30:35 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id j8so3616314pfh.13 for ; Thu, 15 Mar 2018 11:30:35 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id v23-v6si4444768plo.276.2018.03.15.11.30.34 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 15 Mar 2018 11:30:34 -0700 (PDT) Date: Thu, 15 Mar 2018 19:30:31 +0100 From: Michal Hocko Subject: Re: [PATCH] mm/thp: Do not wait for lock_page() in deferred_split_scan() Message-ID: <20180315183031.GS23100@dhcp22.suse.cz> References: <20180315150747.31945-1-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180315150747.31945-1-kirill.shutemov@linux.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Tetsuo Handa , Eric Wheeler On Thu 15-03-18 18:07:47, Kirill A. Shutemov wrote: > deferred_split_scan() gets called from reclaim path. Waiting for page > lock may lead to deadlock there. > > Replace lock_page() with trylock_page() and skip the page if we failed > to lock it. We will get to the page on the next scan. > Fixes: 9a982250f773 ("thp: introduce deferred_split_huge_page()") and maybe even Cc: stable as this can lead to deadlocks AFAICS. Btw. other THP shrinker does suffer from the same problem and a deadlock has been reported[1]. Thanks for Tetsuo to point that out [2]. [1] http://lkml.kernel.org/r/alpine.LRH.2.11.1801242349220.30642@mail.ewheeler.net [2] http://lkml.kernel.org/r/04bbbd39-a1c0-b84b-28a2-0a3876be1054@i-love.sakura.ne.jp > Signed-off-by: Kirill A. Shutemov Anyway feel free to add Acked-by: Michal Hocko to this patch but a deeper audit is due I suspect > --- > mm/huge_memory.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 87ab9b8f56b5..529cf36b7edb 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2783,11 +2783,13 @@ static unsigned long deferred_split_scan(struct shrinker *shrink, > > list_for_each_safe(pos, next, &list) { > page = list_entry((void *)pos, struct page, mapping); > - lock_page(page); > + if (!trylock_page(page)) > + goto next; > /* split_huge_page() removes page from list on success */ > if (!split_huge_page(page)) > split++; > unlock_page(page); > +next: > put_page(page); > } > > -- > 2.16.1 -- Michal Hocko SUSE Labs