linux-kernel - Re: [PATCH 2/9 v2] xfs: introduce and use KM_NOLOCKDEP to silence reclaim lockdep false positives

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Message-ID: <20161216220121.GC7645@dhcp22.suse.cz>
Date:   Fri, 16 Dec 2016 23:01:21 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Brian Foster <bfoster@...hat.com>
Cc:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Chinner <david@...morbit.com>,
        Theodore Ts'o <tytso@....edu>, Chris Mason <clm@...com>,
        David Sterba <dsterba@...e.cz>, Jan Kara <jack@...e.cz>,
        ceph-devel@...r.kernel.org, cluster-devel@...hat.com,
        linux-nfs@...r.kernel.org, logfs@...fs.org,
        linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-btrfs@...r.kernel.org, linux-mtd@...ts.infradead.org,
        reiserfs-devel@...r.kernel.org,
        linux-ntfs-dev@...ts.sourceforge.net,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-afs@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/9 v2] xfs: introduce and use KM_NOLOCKDEP to silence
 reclaim lockdep false positives

On Fri 16-12-16 11:37:50, Brian Foster wrote:
> On Fri, Dec 16, 2016 at 04:40:41PM +0100, Michal Hocko wrote:
> > Updated patch after Mike noticed a BUG_ON when KM_NOLOCKDEP is used.
> > ---
> > From 1497e713e11639157aef21cae29052cb3dc7ab44 Mon Sep 17 00:00:00 2001
> > From: Michal Hocko <mhocko@...e.com>
> > Date: Thu, 15 Dec 2016 13:06:43 +0100
> > Subject: [PATCH] xfs: introduce and use KM_NOLOCKDEP to silence reclaim
> >  lockdep false positives
> > 
> > Now that the page allocator offers __GFP_NOLOCKDEP let's introduce
> > KM_NOLOCKDEP alias for the xfs allocation APIs. While we are at it
> > also change KM_NOFS users introduced by b17cb364dbbb ("xfs: fix missing
> > KM_NOFS tags to keep lockdep happy") and use the new flag for them
> > instead. There is really no reason to make these allocations contexts
> > weaker just because of the lockdep which even might not be enabled
> > in most cases.
> > 
> 
> Hi Michal,
> 
> I haven't gone back to fully grok b17cb364dbbb ("xfs: fix missing
> KM_NOFS tags to keep lockdep happy"), so I'm not really familiar with
> the original problem. FWIW, there was another KM_NOFS instance added by
> that commit in xlog_cil_prepare_log_vecs() that is now in
> xlog_cil_alloc_shadow_bufs(). Perhaps Dave can confirm whether the
> original issue still applies..?

Yes, I've noticed that but the reworked code looked sufficiently
different that I didn't dare to simply convert it.
-- 
Michal Hocko
SUSE Labs