This patch changes the semantics of d_revalidate so that it is always called 
with the parent i_sem lock held.  This allows the autofs4 code to release the
lock if it needs to pend.  Without this patch the autofs has a race condition
in which it pends in the revalidate code while holding the parent i_sem lock 
which prevents the mount from ever completing.  There have been other patches
proposed for this problem which check to see if the parent i_sem lock is held
before releasing it but those solutions ignore the possibility that the lock
may be held by another process.

diff -ur linux-2.6.13.3/fs/autofs4/root.c linux-2.6.13.3-autofspatch/fs/autofs4/root.c
--- linux-2.6.13.3/fs/autofs4/root.c	2005-10-03 16:27:35.000000000 -0700
+++ linux-2.6.13.3-autofspatch/fs/autofs4/root.c	2005-11-28 04:22:52.000000000 -0800
@@ -302,7 +302,9 @@
 		DPRINTK("waiting for expire %p name=%.*s",
 			 dentry, dentry->d_name.len, dentry->d_name.name);
 
+		up(&dentry->d_parent->d_inode->i_sem);
 		status = autofs4_wait(sbi, dentry, NFY_NONE);
+		down(&dentry->d_parent->d_inode->i_sem);
 		
 		DPRINTK("expire done status=%d", status);
 		
@@ -324,7 +326,9 @@
 		DPRINTK("waiting for mount name=%.*s",
 			 dentry->d_name.len, dentry->d_name.name);
 
+		up(&dentry->d_parent->d_inode->i_sem);
 		status = autofs4_wait(sbi, dentry, NFY_MOUNT);
+		down(&dentry->d_parent->d_inode->i_sem);
 		 
 		DPRINTK("mount done status=%d", status);
 
@@ -351,7 +355,9 @@
 		spin_lock(&dentry->d_lock);
 		dentry->d_flags |= DCACHE_AUTOFS_PENDING;
 		spin_unlock(&dentry->d_lock);
+		up(&dentry->d_parent->d_inode->i_sem);
 		status = autofs4_wait(sbi, dentry, NFY_MOUNT);
+		down(&dentry->d_parent->d_inode->i_sem);
 
 		DPRINTK("mount done status=%d", status);
 
diff -ur linux-2.6.13.3/fs/namei.c linux-2.6.13.3-autofspatch/fs/namei.c
--- linux-2.6.13.3/fs/namei.c	2005-10-03 16:27:35.000000000 -0700
+++ linux-2.6.13.3-autofspatch/fs/namei.c	2005-11-28 04:22:52.000000000 -0800
@@ -393,7 +393,6 @@
 	struct dentry * result;
 	struct inode *dir = parent->d_inode;
 
-	down(&dir->i_sem);
 	/*
 	 * First re-do the cached lookup just in case it was created
 	 * while we waited for the directory semaphore..
@@ -419,7 +418,6 @@
 			else
 				result = dentry;
 		}
-		up(&dir->i_sem);
 		return result;
 	}
 
@@ -427,7 +425,6 @@
 	 * Uhhuh! Nasty case: the cache was re-populated while
 	 * we waited on the semaphore. Need to revalidate.
 	 */
-	up(&dir->i_sem);
 	if (result->d_op && result->d_op->d_revalidate) {
 		if (!result->d_op->d_revalidate(result, nd) && !d_invalidate(result)) {
 			dput(result);
@@ -676,13 +673,16 @@
 		     struct path *path)
 {
 	struct vfsmount *mnt = nd->mnt;
+	struct inode *parent = nd->dentry->d_inode;
 	struct dentry *dentry = __d_lookup(nd->dentry, name);
 
+	down(&parent->i_sem);
 	if (!dentry)
 		goto need_lookup;
 	if (dentry->d_op && dentry->d_op->d_revalidate)
 		goto need_revalidate;
 done:
+	up(&parent->i_sem);
 	path->mnt = mnt;
 	path->dentry = dentry;
 	__follow_mount(path);
@@ -703,6 +703,7 @@
 	goto need_lookup;
 
 fail:
+	up(&parent->i_sem);
 	return PTR_ERR(dentry);
 }
 
@@ -718,7 +719,7 @@
 {
 	struct path next;
 	struct inode *inode;
-	int err;
+	int err, reval;
 	unsigned int lookup_flags = nd->flags;
 	
 	while (*name=='/')
@@ -893,9 +894,17 @@
 		 */
 		if (nd->dentry && nd->dentry->d_sb &&
 		    (nd->dentry->d_sb->s_type->fs_flags & FS_REVAL_DOT)) {
+			struct dentry *nparent;
+
 			err = -ESTALE;
 			/* Note: we do not d_invalidate() */
-			if (!nd->dentry->d_op->d_revalidate(nd->dentry, nd))
+			/* Revalidate requires us to lock the parent.
+			 */
+			nparent = nd->dentry->d_parent;
+			down(&nparent->d_inode->i_sem);
+			reval = nd->dentry->d_op->d_revalidate(nd->dentry, nd);
+			up(&nparent->d_inode->i_sem);
+			if (!reval)
 				break;
 		}
 return_base: