linux-kernel - [PATCH v2 4/4] dcache: don't need to take d_lock in prepend

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Message-Id: <1365181061-30787-5-git-send-email-Waiman.Long@hp.com>
Date:	Fri,  5 Apr 2013 12:57:41 -0400
From:	Waiman Long <Waiman.Long@...com>
To:	Alexander Viro <viro@...iv.linux.org.uk>,
	Jeff Layton <jlayton@...hat.com>,
	Miklos Szeredi <mszeredi@...e.cz>, Ian Kent <raven@...maw.net>,
	Sage Weil <sage@...tank.com>, Steve French <sfrench@...ba.org>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Eric Paris <eparis@...hat.com>
Cc:	Waiman Long <Waiman.Long@...com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, autofs@...r.kernel.org,
	ceph-devel@...r.kernel.org, linux-cifs@...r.kernel.org,
	samba-technical@...ts.samba.org, linux-nfs@...r.kernel.org,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>,
	Andi Kleen <andi@...stfloor.org>,
	Dave Chinner <david@...morbit.com>
Subject: [PATCH v2 4/4] dcache: don't need to take d_lock in prepend_path()

The d_lock was used in prepend_path() to protect dentry->d_name from
being changed under the hood. As the caller of prepend_path() has
to take the rename_lock before calling into it, there is no chance
that d_name will be changed. The d_lock lock is only needed when the
rename_lock is not taken.

Signed-off-by: Waiman Long <Waiman.Long@...com>
---
 fs/dcache.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 9477d80..e3d6543 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2529,6 +2529,7 @@ static int prepend_name(char **buffer, int *buflen, struct qstr *name)
  * @buflen: pointer to buffer length
  *
  * Caller holds the rename_lock.
+ * There is no need to lock the dentry as its name cannot be changed.
  */
 static int prepend_path(const struct path *path,
 			const struct path *root,
@@ -2555,9 +2556,7 @@ static int prepend_path(const struct path *path,
 		}
 		parent = dentry->d_parent;
 		prefetch(parent);
-		spin_lock(&dentry->d_lock);
 		error = prepend_name(buffer, buflen, &dentry->d_name);
-		spin_unlock(&dentry->d_lock);
 		if (!error)
 			error = prepend(buffer, buflen, "/", 1);
 		if (error)
-- 
1.7.1

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