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

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Date:	Tue, 19 Feb 2013 13:50:59 -0500
From:	Waiman Long <Waiman.Long@...com>
To:	linux-fsdevel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>
Cc:	Waiman Long <Waiman.Long@...com>, linux-kernel@...r.kernel.org
Subject: [PATCH 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 b1487e2..0e911fc 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2547,6 +2547,7 @@ 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,
@@ -2573,9 +2574,7 @@ 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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