NFS: Reduce time spent holding the i_mutex during fallocate()

At the very least, we should not be taking the i_mutex until after
checking if the server even supports ALLOCATE or DEALLOCATE, allowing
v4.0 or v4.1 to exit without potentially waiting on a lock.
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/nfs42proc.c

@@ -96,9 +96,13 @@ int nfs42_proc_allocate(struct file *filep, loff_t offset, loff_t len)
 	if (!nfs_server_capable(inode, NFS_CAP_ALLOCATE))
 		return -EOPNOTSUPP;
 
+	mutex_lock(&inode->i_mutex);
+
 	err = nfs42_proc_fallocate(&msg, filep, offset, len);
 	if (err == -EOPNOTSUPP)
 		NFS_SERVER(inode)->caps &= ~NFS_CAP_ALLOCATE;
+
+	mutex_unlock(&inode->i_mutex);
 	return err;
 }
 
@@ -114,11 +118,15 @@ int nfs42_proc_deallocate(struct file *filep, loff_t offset, loff_t len)
 		return -EOPNOTSUPP;
 
 	nfs_wb_all(inode);
+	mutex_lock(&inode->i_mutex);
+
 	err = nfs42_proc_fallocate(&msg, filep, offset, len);
 	if (err == 0)
 		truncate_pagecache_range(inode, offset, (offset + len) -1);
 	if (err == -EOPNOTSUPP)
 		NFS_SERVER(inode)->caps &= ~NFS_CAP_DEALLOCATE;
+
+	mutex_unlock(&inode->i_mutex);
 	return err;
 }
 

fs/nfs/nfs4file.c

@@ -158,14 +158,9 @@ static long nfs42_fallocate(struct file *filep, int mode, loff_t offset, loff_t
 	if (ret < 0)
 		return ret;
 
-	mutex_lock(&inode->i_mutex);
 	if (mode & FALLOC_FL_PUNCH_HOLE)
-		ret = nfs42_proc_deallocate(filep, offset, len);
-	else
-		ret = nfs42_proc_allocate(filep, offset, len);
-	mutex_unlock(&inode->i_mutex);
-
-	return ret;
+		return nfs42_proc_deallocate(filep, offset, len);
+	return nfs42_proc_allocate(filep, offset, len);
 }
 #endif /* CONFIG_NFS_V4_2 */