linux-kernel - Re: Commit "new primitive: discard_new

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Message-ID: <20180801162739.GQ30522@ZenIV.linux.org.uk>
Date:   Wed, 1 Aug 2018 17:27:39 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Commit "new primitive: discard_new_inode()" introduces a problem

On Wed, Aug 01, 2018 at 05:16:48PM +0100, Al Viro wrote:
> On Wed, Aug 01, 2018 at 05:11:51PM +0100, Al Viro wrote:
> > On Wed, Aug 01, 2018 at 06:43:56PM +0300, Kirill Tkhai wrote:
> > > #git status
> > > HEAD detached at 22dc9a168272
> > 
> > Wait a sec - just that commit?  With discard_new_inode() not even
> > used anywhere?  Then any of those -ENOMEM is disguised ERR_PTR(-ESTALE)
> > from find_inode()/find_inode_fast(), i.e. an inode found by
> > iget5_locked() (your /etc is on ext4) with I_CREATING still set.
> 
> iget_locked(), that is.
> 
> > And that is set only by insert_inode_locked()/insert_inode_locked4(),
> > and only until unlock_new_inode().
> > 
> > Could you slap WARN_ON(1) before these return ERR_PTR(-ESTALE) in
> > find_inode{,_fast}() and see if that's what's getting triggered?

... and I still can't reproduce it here - exact same tree, same .config,
same reproducer.  The only difference is that it's a gcc-5 build, but
I can do gcc-6 as well; doubt that it'll change anything.