[PATCH] NFS4: fix for recursive locking problem

When I was performing some operations on NFS, I got below error on server
side.

  =============================================
  [ INFO: possible recursive locking detected ]
  2.6.19-prep #1
  ---------------------------------------------
  nfsd4/3525 is trying to acquire lock:
   (&inode->i_mutex){--..}, at: [<c0611e5a>] mutex_lock+0x21/0x24

  but task is already holding lock:
   (&inode->i_mutex){--..}, at: [<c0611e5a>] mutex_lock+0x21/0x24

  other info that might help us debug this:
  2 locks held by nfsd4/3525:
   #0:  (client_mutex){--..}, at: [<c0611e5a>] mutex_lock+0x21/0x24
   #1:  (&inode->i_mutex){--..}, at: [<c0611e5a>] mutex_lock+0x21/0x24

  stack backtrace:
   [<c04051ed>] show_trace_log_lvl+0x58/0x16a
   [<c04057fa>] show_trace+0xd/0x10
   [<c0405913>] dump_stack+0x19/0x1b
   [<c043b6f1>] __lock_acquire+0x778/0x99c
   [<c043be86>] lock_acquire+0x4b/0x6d
   [<c0611ceb>] __mutex_lock_slowpath+0xbc/0x20a
   [<c0611e5a>] mutex_lock+0x21/0x24
   [<c047fd7e>] vfs_rmdir+0x76/0xf8
   [<f94b7ce9>] nfsd4_clear_clid_dir+0x2c/0x41 [nfsd]
   [<f94b7de9>] nfsd4_remove_clid_dir+0xb1/0xe8 [nfsd]
   [<f94b307b>] laundromat_main+0x9b/0x1c3 [nfsd]
   [<c04333d6>] run_workqueue+0x7a/0xbb
   [<c0433d0b>] worker_thread+0xd2/0x107
   [<c0436285>] kthread+0xc3/0xf2
   [<c0402005>] kernel_thread_helper+0x5/0xb
  ===================================================================

Cause for this problem was,2 successive mutex_lock calls on 2 diffrent inodes ,as shown below

	static int
	nfsd4_clear_clid_dir(struct dentry *dir, struct dentry *dentry)
	{
	        int status;

	        /* For now this directory should already be empty, but we empty it of
        	 * any regular files anyway, just in case the directory was created by
	         * a kernel from the future.... */
        	nfsd4_list_rec_dir(dentry, nfsd4_remove_clid_file);
	        mutex_lock(&dir->d_inode->i_mutex);
	        status = vfs_rmdir(dir->d_inode, dentry);
	...

	int vfs_rmdir(struct inode *dir, struct dentry *dentry)
	{
	        int error = may_delete(dir, dentry, 1);

	        if (error)
	                return error;

	        if (!dir->i_op || !dir->i_op->rmdir)
        	        return -EPERM;

	        DQUOT_INIT(dir);

	        mutex_lock(&dentry->d_inode->i_mutex);
	...

So I have developed the patch to overcome this problem.
Signed-off-by: NSrinivasa DS <srinivasa@in.ibm.com>
Cc: Neil Brown <neilb@suse.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

fs/nfsd/nfs4recover.c

@@ -274,7 +274,7 @@ nfsd4_clear_clid_dir(struct dentry *dir, struct dentry *dentry)
 	 * any regular files anyway, just in case the directory was created by
 	 * a kernel from the future.... */
 	nfsd4_list_rec_dir(dentry, nfsd4_remove_clid_file);
-	mutex_lock(&dir->d_inode->i_mutex);
+	mutex_lock_nested(&dir->d_inode->i_mutex, I_MUTEX_PARENT);
 	status = vfs_rmdir(dir->d_inode, dentry);
 	mutex_unlock(&dir->d_inode->i_mutex);
 	return status;