linux-kernel - [PATCH] autofs4: use ACCESS_ONCE rather than rcu_dereference for dentry->d

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Message-ID: <20140903140617.7502ad32@notabene.brown>
Date:	Wed, 3 Sep 2014 14:06:17 +1000
From:	NeilBrown <neilb@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	kbuild-all@...org, lkml <linux-kernel@...r.kernel.org>,
	Ian Kent <raven@...maw.net>, autofs@...r.kernel.org
Subject: [PATCH] autofs4: use ACCESS_ONCE rather than rcu_dereference for
 dentry->d_inode



As the kbuild test robot reports, rcu_dereference() isn't really
appropriate here - we don't need a memory barrier, just a guard
against accidentally dereferencing NULL.

This can be merged into
 autofs4: d_manage() should return -EISDIR when appropriate in rcu-walk mode.
in 'mm'.

Signed-off-by: NeilBrown <neilb@...e.de>

diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index 71e4413d65c8..d76d083f2f06 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -463,7 +463,7 @@ static int autofs4_d_manage(struct dentry *dentry, bool rcu_walk)
 			return 0;
 		if (d_mountpoint(dentry))
 			return 0;
-		inode = rcu_dereference(dentry->d_inode);
+		inode = ACCESS_ONCE(dentry->d_inode);
 		if (inode && S_ISLNK(inode->i_mode))
 			return -EISDIR;
 		if (list_empty(&dentry->d_subdirs))

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