linux-kernel - Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async fsync

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Message-ID: <20160320015511.GZ17997@ZenIV.linux.org.uk>
Date:	Sun, 20 Mar 2016 01:55:11 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Benjamin LaHaise <bcrl@...ck.org>,
	Dave Chinner <david@...morbit.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-aio@...ck.org, linux-mm <linux-mm@...ck.org>
Subject: Re: aio openat Re: [PATCH 07/13] aio: enabled thread based async
 fsync

On Sat, Mar 19, 2016 at 06:45:19PM -0700, Linus Torvalds wrote:

> It actually does seem to do that, although in an admittedly rather
> questionable way.
> 
> I think it should use path_openat() rather than do_filp_open(), but
> passing in LOOKUP_RCU to do_filp_open() actually does work: it just
> means that the retry after ECHILD/ESTALE will just do it *again* with
> LOOKUP_RCU. It won't fall back to non-rcu mode, it just won't or in
> the LOOKUP_RCU flag that is already set.

What would make unlazy_walk() fail?  And if it succeeds, you are not
in RCU mode anymore *without* restarting from scratch...