cifs: call cifs_update_eof with i_lock held

cifs_update_eof has the potential to be racy if multiple threads are
trying to modify it at the same time. Protect modifications of the
server_eof value with the inode->i_lock.
Signed-off-by: Jeff Layton <jlayton@redhat.com>

fs/cifs/cifsglob.h

@@ -626,7 +626,7 @@ struct cifsInodeInfo {
 	bool delete_pending;		/* DELETE_ON_CLOSE is set */
 	bool invalid_mapping;		/* pagecache is invalid */
 	unsigned long time;		/* jiffies of last update of inode */
-	u64  server_eof;		/* current file size on server */
+	u64  server_eof;		/* current file size on server -- protected by i_lock */
 	u64  uniqueid;			/* server inode number */
 	u64  createtime;		/* creation time on server */
 #ifdef CONFIG_CIFS_FSCACHE

fs/cifs/cifssmb.c

@@ -2044,7 +2044,9 @@ cifs_writev_complete(struct work_struct *work)
 	int i = 0;
 
 	if (wdata->result == 0) {
+		spin_lock(&inode->i_lock);
 		cifs_update_eof(CIFS_I(inode), wdata->offset, wdata->bytes);
+		spin_unlock(&inode->i_lock);
 		cifs_stats_bytes_written(tlink_tcon(wdata->cfile->tlink),
 					 wdata->bytes);
 	} else if (wdata->sync_mode == WB_SYNC_ALL && wdata->result == -EAGAIN)

fs/cifs/file.c

@@ -1399,7 +1399,10 @@ int cifs_lock(struct file *file, int cmd, struct file_lock *flock)
 	return rc;
 }
 
-/* update the file size (if needed) after a write */
+/*
+ * update the file size (if needed) after a write. Should be called with
+ * the inode->i_lock held
+ */
 void
 cifs_update_eof(struct cifsInodeInfo *cifsi, loff_t offset,
 		      unsigned int bytes_written)
@@ -1471,7 +1474,9 @@ static ssize_t cifs_write(struct cifsFileInfo *open_file, __u32 pid,
 				return rc;
 			}
 		} else {
+			spin_lock(&dentry->d_inode->i_lock);
 			cifs_update_eof(cifsi, *poffset, bytes_written);
+			spin_unlock(&dentry->d_inode->i_lock);
 			*poffset += bytes_written;
 		}
 	}
@@ -2197,7 +2202,9 @@ cifs_iovec_write(struct file *file, const struct iovec *iov,
 		if (written) {
 			len -= written;
 			total_written += written;
+			spin_lock(&inode->i_lock);
 			cifs_update_eof(CIFS_I(inode), *poffset, written);
+			spin_unlock(&inode->i_lock);
 			*poffset += written;
 		} else if (rc < 0) {
 			if (!total_written)