linux-kernel - Re: [PATCH v8 01/10] kernfs: Remove reference counting for kernfs_open

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Message-ID: <YmhTFZ5zCGhWJOry@slm.duckdns.org>
Date:   Tue, 26 Apr 2022 10:16:21 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Imran Khan <imran.f.khan@...cle.com>, gregkh@...uxfoundation.org,
        ebiederm@...ssion.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 01/10] kernfs: Remove reference counting for
 kernfs_open_node.

On Tue, Apr 26, 2022 at 08:13:22PM +0000, Al Viro wrote:
> On Tue, Apr 26, 2022 at 08:29:21AM -1000, Tejun Heo wrote:
> 
> > The code is just wrong. You can end up:
> > 
> >         on = kn->attr.open;
> >         if (!on)
> >                 return;
> > 
> >         // we get preempted here and someone else puts @on and then
> >         // recreates it
> 
> Can't happen - the caller has guaranteed that no new openers will be
> coming.  Look at the call chain of kernfs_drain_open_files()...

Ah, okay. It can only transition to NULL from there. It's still a weird way
to go about it tho.

Thanks.

-- 
tejun