NFS: Fix a race in sillyrename

lookup() and sillyrename() can race one another because the sillyrename()
completion cannot take the parent directory's inode->i_mutex since the
latter may be held by whoever is calling dput().

We therefore have little option but to add extra locking to ensure that
nfs_lookup() and nfs_atomic_open() do not race with the sillyrename
completion.
If somebody has looked up the sillyrenamed file in the meantime, we just
transfer the sillydelete information to the new dentry.

Please refer to the bug-report at
	http://bugzilla.linux-nfs.org/show_bug.cgi?id=150

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/dir.c

@@ -562,6 +562,7 @@ static int nfs_readdir(struct file *filp, void *dirent, filldir_t filldir)
 	nfs_fattr_init(&fattr);
 	desc->entry = &my_entry;
 
+	nfs_block_sillyrename(dentry);
 	while(!desc->entry->eof) {
 		res = readdir_search_pagecache(desc);
 
@@ -592,6 +593,7 @@ static int nfs_readdir(struct file *filp, void *dirent, filldir_t filldir)
 			break;
 		}
 	}
+	nfs_unblock_sillyrename(dentry);
 	unlock_kernel();
 	if (res > 0)
 		res = 0;
@@ -866,6 +868,7 @@ struct dentry_operations nfs_dentry_operations = {
 static struct dentry *nfs_lookup(struct inode *dir, struct dentry * dentry, struct nameidata *nd)
 {
 	struct dentry *res;
+	struct dentry *parent;
 	struct inode *inode = NULL;
 	int error;
 	struct nfs_fh fhandle;
@@ -894,26 +897,31 @@ static struct dentry *nfs_lookup(struct inode *dir, struct dentry * dentry, stru
 		goto out_unlock;
 	}
 
+	parent = dentry->d_parent;
+	/* Protect against concurrent sillydeletes */
+	nfs_block_sillyrename(parent);
 	error = NFS_PROTO(dir)->lookup(dir, &dentry->d_name, &fhandle, &fattr);
 	if (error == -ENOENT)
 		goto no_entry;
 	if (error < 0) {
 		res = ERR_PTR(error);
-		goto out_unlock;
+		goto out_unblock_sillyrename;
 	}
 	inode = nfs_fhget(dentry->d_sb, &fhandle, &fattr);
 	res = (struct dentry *)inode;
 	if (IS_ERR(res))
-		goto out_unlock;
+		goto out_unblock_sillyrename;
 
 no_entry:
 	res = d_materialise_unique(dentry, inode);
 	if (res != NULL) {
 		if (IS_ERR(res))
-			goto out_unlock;
+			goto out_unblock_sillyrename;
 		dentry = res;
 	}
 	nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
+out_unblock_sillyrename:
+	nfs_unblock_sillyrename(parent);
 out_unlock:
 	unlock_kernel();
 out:

fs/nfs/inode.c

@@ -1169,6 +1169,9 @@ static void init_once(struct kmem_cache * cachep, void *foo)
 	INIT_RADIX_TREE(&nfsi->nfs_page_tree, GFP_ATOMIC);
 	nfsi->ncommit = 0;
 	nfsi->npages = 0;
+	atomic_set(&nfsi->silly_count, 1);
+	INIT_HLIST_HEAD(&nfsi->silly_list);
+	init_waitqueue_head(&nfsi->waitqueue);
 	nfs4_init_once(nfsi);
 }
 

fs/nfs/nfs4proc.c

@@ -1372,6 +1372,7 @@ out_close:
 struct dentry *
 nfs4_atomic_open(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
 {
+	struct dentry *parent;
 	struct path path = {
 		.mnt = nd->mnt,
 		.dentry = dentry,
@@ -1394,6 +1395,9 @@ nfs4_atomic_open(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
 	cred = rpcauth_lookupcred(NFS_CLIENT(dir)->cl_auth, 0);
 	if (IS_ERR(cred))
 		return (struct dentry *)cred;
+	parent = dentry->d_parent;
+	/* Protect against concurrent sillydeletes */
+	nfs_block_sillyrename(parent);
 	state = nfs4_do_open(dir, &path, nd->intent.open.flags, &attr, cred);
 	put_rpccred(cred);
 	if (IS_ERR(state)) {
@@ -1401,12 +1405,14 @@ nfs4_atomic_open(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
 			d_add(dentry, NULL);
 			nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
 		}
+		nfs_unblock_sillyrename(parent);
 		return (struct dentry *)state;
 	}
 	res = d_add_unique(dentry, igrab(state->inode));
 	if (res != NULL)
 		path.dentry = res;
 	nfs_set_verifier(path.dentry, nfs_save_change_attribute(dir));
+	nfs_unblock_sillyrename(parent);
 	nfs4_intent_set_file(nd, &path, state);
 	return res;
 }

fs/nfs/unlink.c

@@ -14,6 +14,7 @@
 
 
 struct nfs_unlinkdata {
+	struct hlist_node list;
 	struct nfs_removeargs args;
 	struct nfs_removeres res;
 	struct inode *dir;
@@ -52,6 +53,20 @@ static int nfs_copy_dname(struct dentry *dentry, struct nfs_unlinkdata *data)
 	return 0;
 }
 
+static void nfs_free_dname(struct nfs_unlinkdata *data)
+{
+	kfree(data->args.name.name);
+	data->args.name.name = NULL;
+	data->args.name.len = 0;
+}
+
+static void nfs_dec_sillycount(struct inode *dir)
+{
+	struct nfs_inode *nfsi = NFS_I(dir);
+	if (atomic_dec_return(&nfsi->silly_count) == 1)
+		wake_up(&nfsi->waitqueue);
+}
+
 /**
  * nfs_async_unlink_init - Initialize the RPC info
  * task: rpc_task of the sillydelete
@@ -95,6 +110,8 @@ static void nfs_async_unlink_done(struct rpc_task *task, void *calldata)
 static void nfs_async_unlink_release(void *calldata)
 {
 	struct nfs_unlinkdata	*data = calldata;
+
+	nfs_dec_sillycount(data->dir);
 	nfs_free_unlinkdata(data);
 }
 
@@ -104,33 +121,100 @@ static const struct rpc_call_ops nfs_unlink_ops = {
 	.rpc_release = nfs_async_unlink_release,
 };
 
-static int nfs_call_unlink(struct dentry *dentry, struct nfs_unlinkdata *data)
+static int nfs_do_call_unlink(struct dentry *parent, struct inode *dir, struct nfs_unlinkdata *data)
 {
 	struct rpc_task *task;
+	struct dentry *alias;
+
+	alias = d_lookup(parent, &data->args.name);
+	if (alias != NULL) {
+		int ret = 0;
+		/*
+		 * Hey, we raced with lookup... See if we need to transfer
+		 * the sillyrename information to the aliased dentry.
+		 */
+		nfs_free_dname(data);
+		spin_lock(&alias->d_lock);
+		if (!(alias->d_flags & DCACHE_NFSFS_RENAMED)) {
+			alias->d_fsdata = data;
+			alias->d_flags ^= DCACHE_NFSFS_RENAMED;
+			ret = 1;
+		}
+		spin_unlock(&alias->d_lock);
+		nfs_dec_sillycount(dir);
+		dput(alias);
+		return ret;
+	}
+	data->dir = igrab(dir);
+	if (!data->dir) {
+		nfs_dec_sillycount(dir);
+		return 0;
+	}
+	data->args.fh = NFS_FH(dir);
+	nfs_fattr_init(&data->res.dir_attr);
+
+	task = rpc_run_task(NFS_CLIENT(dir), RPC_TASK_ASYNC, &nfs_unlink_ops, data);
+	if (!IS_ERR(task))
+		rpc_put_task(task);
+	return 1;
+}
+
+static int nfs_call_unlink(struct dentry *dentry, struct nfs_unlinkdata *data)
+{
 	struct dentry *parent;
 	struct inode *dir;
+	int ret = 0;
 
-	if (nfs_copy_dname(dentry, data) < 0)
-		goto out_free;
 
 	parent = dget_parent(dentry);
 	if (parent == NULL)
 		goto out_free;
-	dir = igrab(parent->d_inode);
+	dir = parent->d_inode;
+	if (nfs_copy_dname(dentry, data) == 0)
+		goto out_dput;
+	/* Non-exclusive lock protects against concurrent lookup() calls */
+	spin_lock(&dir->i_lock);
+	if (atomic_inc_not_zero(&NFS_I(dir)->silly_count) == 0) {
+		/* Deferred delete */
+		hlist_add_head(&data->list, &NFS_I(dir)->silly_list);
+		spin_unlock(&dir->i_lock);
+		ret = 1;
+		goto out_dput;
+	}
+	spin_unlock(&dir->i_lock);
+	ret = nfs_do_call_unlink(parent, dir, data);
+out_dput:
 	dput(parent);
-	if (dir == NULL)
-		goto out_free;
+out_free:
+	return ret;
+}
 
-	data->dir = dir;
-	data->args.fh = NFS_FH(dir);
-	nfs_fattr_init(&data->res.dir_attr);
+void nfs_block_sillyrename(struct dentry *dentry)
+{
+	struct nfs_inode *nfsi = NFS_I(dentry->d_inode);
 
-	task = rpc_run_task(NFS_CLIENT(dir), RPC_TASK_ASYNC, &nfs_unlink_ops, data);
-	if (!IS_ERR(task))
-		rpc_put_task(task);
-	return 1;
-out_free:
-	return 0;
+	wait_event(nfsi->waitqueue, atomic_cmpxchg(&nfsi->silly_count, 1, 0) == 1);
+}
+
+void nfs_unblock_sillyrename(struct dentry *dentry)
+{
+	struct inode *dir = dentry->d_inode;
+	struct nfs_inode *nfsi = NFS_I(dir);
+	struct nfs_unlinkdata *data;
+
+	atomic_inc(&nfsi->silly_count);
+	spin_lock(&dir->i_lock);
+	while (!hlist_empty(&nfsi->silly_list)) {
+		if (!atomic_inc_not_zero(&nfsi->silly_count))
+			break;
+		data = hlist_entry(nfsi->silly_list.first, struct nfs_unlinkdata, list);
+		hlist_del(&data->list);
+		spin_unlock(&dir->i_lock);
+		if (nfs_do_call_unlink(dentry, dir, data) == 0)
+			nfs_free_unlinkdata(data);
+		spin_lock(&dir->i_lock);
+	}
+	spin_unlock(&dir->i_lock);
 }
 
 /**

include/linux/nfs_fs.h

@@ -160,6 +160,12 @@ struct nfs_inode {
 	/* Open contexts for shared mmap writes */
 	struct list_head	open_files;
 
+	/* Number of in-flight sillydelete RPC calls */
+	atomic_t		silly_count;
+	/* List of deferred sillydelete requests */
+	struct hlist_head	silly_list;
+	wait_queue_head_t	waitqueue;
+
 #ifdef CONFIG_NFS_V4
 	struct nfs4_cached_acl	*nfs4_acl;
         /* NFSv4 state */
@@ -394,6 +400,8 @@ extern void nfs_release_automount_timer(void);
  */
 extern int  nfs_async_unlink(struct inode *dir, struct dentry *dentry);
 extern void nfs_complete_unlink(struct dentry *dentry, struct inode *);
+extern void nfs_block_sillyrename(struct dentry *dentry);
+extern void nfs_unblock_sillyrename(struct dentry *dentry);
 
 /*
  * linux/fs/nfs/write.c