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Date: Mon, 9 Sep 2013 20:10:29 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Waiman Long <waiman.long@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
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        George Spelvin <linux@horizon.com>, John Stoffel <john@stoffel.org>
Subject: Re: [PATCH v4 1/1] dcache: Translating dentry into pathname without
 taking rename_lock
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On Mon, Sep 09, 2013 at 02:46:57PM -0400, Waiman Long wrote:

> I am fine with your proposed change as long as it gets the job done.

I suspect that the real problem is the unlock part of read_seqretry_or_unlock();
for d_walk() we want to be able to check if we need retry and continue walking
if we do not.  Let's do it that way: I've applied your patch as is, with the
next step being
	* split read_seqretry_or_unlock():
need_seqretry() (return (!(seq & 1) && read_seqretry(lock, seq))
done_seqretry() (if (seq & 1) write_sequnlock(lock, seq)),
your if (read_seqretry_or_unlock(&rename_lock, &seq))
		goto restart;
becoming
	if (need_seqretry(&rename_lock, seq)) {
		seq = 1;
		goto restart;
	}
	done_seqretry(&rename_lock, seq);

Then d_walk() is trivially massaged to use of read_seqbegin_or_lock(),
need_seqretry() and done_seqretry().  Give me a few, I'll post it...