From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752270AbdDCIrg (ORCPT ); Mon, 3 Apr 2017 04:47:36 -0400 Received: from mx2.suse.de ([195.135.220.15]:59347 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752013AbdDCIre (ORCPT ); Mon, 3 Apr 2017 04:47:34 -0400 Date: Mon, 3 Apr 2017 10:47:31 +0200 From: Michal Hocko To: Shakeel Butt Cc: Andrey Ryabinin , Seth Jennings , Dan Streetman , Linux MM , LKML , Andrew Morton Subject: Re: [PATCH] mm/zswap: fix potential deadlock in zswap_frontswap_store() Message-ID: <20170403084729.GG24661@dhcp22.suse.cz> References: <20170331153009.11397-1-aryabinin@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 31-03-17 10:00:30, Shakeel Butt wrote: > On Fri, Mar 31, 2017 at 8:30 AM, Andrey Ryabinin > wrote: > > zswap_frontswap_store() is called during memory reclaim from > > __frontswap_store() from swap_writepage() from shrink_page_list(). > > This may happen in NOFS context, thus zswap shouldn't use __GFP_FS, > > otherwise we may renter into fs code and deadlock. > > zswap_frontswap_store() also shouldn't use __GFP_IO to avoid recursion > > into itself. > > > > Is it possible to enter fs code (or IO) from zswap_frontswap_store() > other than recursive memory reclaim? However recursive memory reclaim > is protected through PF_MEMALLOC task flag. The change seems fine but > IMHO reasoning needs an update. Adding Michal for expert opinion. Yes this is true. I haven't checked all the callers of zswap_frontswap_store but is it fixing any real problem or just trying to be overly cautious. Btw... > > zswap_frontswap_store() call zpool_malloc() with __GFP_NORETRY | > > __GFP_NOWARN | __GFP_KSWAPD_RECLAIM, so let's use the same flags for > > zswap_entry_cache_alloc() as well, instead of GFP_KERNEL. > > > > Signed-off-by: Andrey Ryabinin > > --- > > mm/zswap.c | 7 +++---- > > 1 file changed, 3 insertions(+), 4 deletions(-) > > > > diff --git a/mm/zswap.c b/mm/zswap.c > > index eedc278..12ad7e9 100644 > > --- a/mm/zswap.c > > +++ b/mm/zswap.c > > @@ -966,6 +966,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, > > struct zswap_tree *tree = zswap_trees[type]; > > struct zswap_entry *entry, *dupentry; > > struct crypto_comp *tfm; > > + gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM; This doesn't trigger direct reclaim so __GFP_NORETRY is bogus. I suspect you didn't want GFP_NOWAIT alternative. [...] > > @@ -1017,9 +1018,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, > > > > /* store */ > > len = dlen + sizeof(struct zswap_header); > > - ret = zpool_malloc(entry->pool->zpool, len, > > - __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM, > > - &handle); > > + ret = zpool_malloc(entry->pool->zpool, len, gfp, &handle); and here we used to do GFP_NOWAIT alternative already. What is going on here? > > if (ret == -ENOSPC) { > > zswap_reject_compress_poor++; > > goto put_dstmem; > > -- > > 2.10.2 > > -- Michal Hocko SUSE Labs