From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753165AbeDIPgp (ORCPT ); Mon, 9 Apr 2018 11:36:45 -0400 Received: from mx2.suse.de ([195.135.220.15]:55435 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751623AbeDIPgn (ORCPT ); Mon, 9 Apr 2018 11:36:43 -0400 Date: Mon, 9 Apr 2018 17:34:09 +0200 From: David Sterba To: Michal Hocko Cc: Matthew Wilcox , Chao Yu , Minchan Kim , Jaegeuk Kim , Christopher Lameter , Andrew Morton , linux-mm , LKML , Johannes Weiner , Jan Kara , Chris Fries , linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] mm: workingset: fix NULL ptr dereference Message-ID: <20180409153409.nqsklemu3igacgbj@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Michal Hocko , Matthew Wilcox , Chao Yu , Minchan Kim , Jaegeuk Kim , Christopher Lameter , Andrew Morton , linux-mm , LKML , Johannes Weiner , Jan Kara , Chris Fries , linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org References: <20180409015815.235943-1-minchan@kernel.org> <20180409024925.GA21889@bombadil.infradead.org> <20180409030930.GA214930@rodete-desktop-imager.corp.google.com> <20180409111403.GA31652@bombadil.infradead.org> <20180409112514.GA195937@rodete-laptop-imager.corp.google.com> <7706245c-2661-f28b-f7f9-8f11e1ae932b@huawei.com> <20180409124852.GE21835@dhcp22.suse.cz> <20180409134114.GA30963@bombadil.infradead.org> <20180409135215.GH21835@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180409135215.GH21835@dhcp22.suse.cz> User-Agent: NeoMutt/20180323 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 09, 2018 at 03:52:15PM +0200, Michal Hocko wrote: > On Mon 09-04-18 06:41:14, Matthew Wilcox wrote: > > On Mon, Apr 09, 2018 at 02:48:52PM +0200, Michal Hocko wrote: > > > On Mon 09-04-18 20:25:06, Chao Yu wrote: > > > [...] > > > > diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c > > > > index c85cccc2e800..cc63f8c448f0 100644 > > > > --- a/fs/f2fs/inode.c > > > > +++ b/fs/f2fs/inode.c > > > > @@ -339,10 +339,10 @@ struct inode *f2fs_iget(struct super_block *sb, unsigned long ino) > > > > make_now: > > > > if (ino == F2FS_NODE_INO(sbi)) { > > > > inode->i_mapping->a_ops = &f2fs_node_aops; > > > > - mapping_set_gfp_mask(inode->i_mapping, GFP_F2FS_ZERO); > > > > + mapping_set_gfp_mask(inode->i_mapping, GFP_NOFS); > > > > > > An unrelated question. Why do you make all allocations for the mapping > > > NOFS automatically? What kind of reclaim recursion problems are you > > > trying to prevent? > > > > It's worth noting that this is endemic in filesystems. > > Yes, and I have strong suspicion that this is a mindless copy&pasting... > Well, xfs had a good reason for it in the past - mostly to handle deep > call stacks on complicated storage setups in the past when we used to > trigger IO from the direct reclaim. I am not sure whether there are > other reasons to keep the status quo except for finding somebody brave > enough to post the patch, do all the due testing. > > > $ git grep mapping_set_gfp_mask.*FS > > drivers/block/loop.c: mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS)); > > fs/btrfs/disk-io.c: mapping_set_gfp_mask(fs_info->btree_inode->i_mapping, GFP_NOFS); Thi was added in 1561deda687eef0 (https://git.kernel.org/linus/1561deda687eef0e9506) and probably after a deadlock report. The changelog mentions the potential recursion from fs -> allocation -> fs, but I'm not sure if this still happens on the MM side today. For the filesystem part, I think the key functions of the callchain are still there. The code was been added in 2011 and the 2nd hunk of the patch added a code that's not present today AFAICS, so this is worth revisiting. I still don't understand how it's related to the GFP_HIGHUSER_MOVABLE, this patch is from time where the metadata pages were possibly allocated from HIGHMEM but this was removed later in a65917156e345946db (https://git.kernel.org/linus/a65917156e345946db).