This modifies sysfs_drop_dentry so it no longers needs the
sysfs_assoc_lock and it's assorted challenges. 

The principal idea is that __sysfs_get_dentry when not creating dentry
will return a dentry for the sysfs_dirent if there is one in the
dcache.   If we do get a dentry we can drop it and force it out
of the cache.

For good measure I am also calling shrink_dcache_parent which will
force all of the child dentries out of the dcache as well if it
is a directory.

This is essentially and adaption of proc_flush_task from procfs
to handle the similar problems of sysfs.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
 fs/sysfs/dir.c |   34 ++++++++++++----------------------
 1 files changed, 12 insertions(+), 22 deletions(-)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index ed2e6f3..f8de6fb 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -516,35 +516,25 @@ void sysfs_remove_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
  *	parent on entry to this function such that it can't be looked
  *	up anymore.
  *
- *	@sd->s_dentry which is protected with sysfs_assoc_lock points
- *	to the currently associated dentry but we're not holding a
- *	reference to it and racing with dput().  Grab dcache_lock and
- *	verify dentry before dropping it.  If @sd->s_dentry is NULL or
- *	dput() beats us, no need to bother.
+ *	We find the dentry for @sd by probing the dcache while holding
+ *	sysfs_mutex to keep it from changing until we are done.
  */
 static void sysfs_drop_dentry(struct sysfs_dirent *sd)
 {
 	struct dentry *dentry = NULL;
 	struct inode *inode;
 
-	/* We're not holding a reference to ->s_dentry dentry but the
-	 * field will stay valid as long as sysfs_assoc_lock is held.
-	 */
-	spin_lock(&sysfs_assoc_lock);
-	spin_lock(&dcache_lock);
-
-	/* drop dentry if it's there and dput() didn't kill it yet */
-	if (sd->s_dentry && sd->s_dentry->d_inode) {
-		dentry = dget_locked(sd->s_dentry);
-		spin_lock(&dentry->d_lock);
-		__d_drop(dentry);
-		spin_unlock(&dentry->d_lock);
+	/* Remove a dentry for a sd from the dcache if present */
+	mutex_lock(&sysfs_mutex);
+	dentry = __sysfs_get_dentry(sd, 0);
+	if (IS_ERR(dentry))
+		dentry = NULL;
+	if (dentry) {
+		shrink_dcache_parent(dentry);
+		d_drop(dentry);
+		dput(dentry);
 	}
-
-	spin_unlock(&dcache_lock);
-	spin_unlock(&sysfs_assoc_lock);
-
-	dput(dentry);
+	mutex_unlock(&sysfs_mutex);
 
 	/* adjust nlink and update timestamp */
 	inode = ilookup(sysfs_sb, sd->s_ino);
-- 
1.5.1.1.181.g2de0

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