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Date:   Tue, 24 Sep 2019 17:33:01 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Josef Bacik <josef@toxicpanda.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        "zhengbin (A)" <zhengbin13@huawei.com>, Jan Kara <jack@suse.cz>,
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        "Yan, Zheng" <zyan@redhat.com>, linux-cifs@vger.kernel.org,
        Steve French <sfrench@us.ibm.com>
Subject: Re: [PATCH] Re: Possible FS race condition between iterate_dir and
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On Tue, Sep 24, 2019 at 11:26:28AM -0400, Josef Bacik wrote:
> On Tue, Sep 24, 2019 at 04:11:07PM +0100, Al Viro wrote:
> > On Tue, Sep 24, 2019 at 11:01:45AM -0400, Josef Bacik wrote:
> > 
> > > Sorry I mis-read the code a little bit.  This is purely for the subvolume link
> > > directories.  We haven't wandered down into this directory yet.  If the
> > > subvolume is being deleted and we still have the fake directory entry for it
> > > then we just populate it with this dummy inode and then we can't lookup anything
> > > underneath it.  Thanks,
> > 
> > Umm...  OK, I guess my question would be better stated a bit differently: we
> > have a directory inode, with btrfs_lookup() for lookups in it *and* with
> > dcache_readdir() called when you try to do getdents(2) on that thing.
> > How does that work?
> 
> Sorry I hadn't read through the context.  We won't end up with things under this
> directory.  The lookup will try to look up into the subvolume, see that it's
> empty, and just return nothing.  There should never be any entries that end up
> under this dummy entry.  Thanks,

Er...  Then why not use simple_lookup() in there?  Confused...