linux-kernel - Re: More parallel atomic_open/d_splice_alias fun with NFS and possibly more FSes.

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Message-ID: <20160705180841.GO14480@ZenIV.linux.org.uk>
Date:	Tue, 5 Jul 2016 19:08:41 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Oleg Drokin <green@...uxhacker.ru>
Cc:	Mailing List <linux-kernel@...r.kernel.org>,
	"<linux-fsdevel@...r.kernel.org>" <linux-fsdevel@...r.kernel.org>
Subject: Re: More parallel atomic_open/d_splice_alias fun with NFS and
 possibly more FSes.

On Tue, Jul 05, 2016 at 12:33:09PM -0400, Oleg Drokin wrote:

> This also makes me question the whole thing some more. We are definitely in lookup
> when this hits, so the dentry is already new, yet it does not check off as
> d_in_lookup(). That also means that by skipping the ll_splice_alias we are failing
> to hash it and that causing needless lookups later?
> Looking some back into the history of commits, d_in_lookup() is to tell us
> that we are in the middle of lookup. How can we be in the middle of lookup
> path then and not have this set on a dentry? We know dentry was not
> substituted with anything here because we did not call into ll_split_alias().
> So what's going on then?

Lookup in directory locked exclusive, that's what...  In unlink(), in your
testcase.  And yes, this piece of 1/3 is incorrect; what I do not understand
is the logics of what you are doing with dcache in ll_splice_alias() and
in its caller ;-/