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>

1 files changed, 99 insertions, 15 deletions

diff --git a/fs/nfs/unlink.c b/fs/nfs/unlink.c
index 1aed850d18f2..6ecd46c967c8 100644
--- a/fs/nfs/unlink.c
+++ b/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);
 }
 
 /**