linux-kernel - Re: [PATCH v4 1/1] dcache: Translating dentry into pathname without taking rename

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Message-ID: <CALkWK0ko21Xx9Dtbtk8FYvYxy6TWM8ncmO5MQ1A0L4HMCsPadw@mail.gmail.com>
Date:	Tue, 10 Sep 2013 08:42:57 +0530
From:	Ramkumar Ramachandra <artagnon@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	George Spelvin <linux@...izon.com>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	John Stoffel <john@...ffel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Norton, Scott J" <scott.norton@...com>,
	Waiman Long <Waiman.Long@...com>
Subject: Re: [PATCH v4 1/1] dcache: Translating dentry into pathname without
 taking rename_lock

Linus Torvalds wrote:
> It doesn't need to. The RCU lookup looks at individual dentry sequence
> numbers and doesn't care about the bigger rename sequence number at
> all.

Right; it's sequential.

> The fallback (if you hit one of the very very rare races, or if you
> hit a symlink) ends up doing per-path-component lookups under the
> rename sequence lock, but for it, read-locking it until it succeeds is
> the right thing to do.

No, it's write-locking.
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