ext4: Fix race between migration and mmap write

[linux-2.6-omap-h63xx.git] / fs / ext4 / migrate.c

diff --git a/fs/ext4/migrate.c b/fs/ext4/migrate.c
index 5c1e27de7755b46552c3fd85dd11ad66d0ec1490..9b4fb07d192c28ff07b32a5bd76e1c2b789a9e41 100644 (file)
--- a/fs/ext4/migrate.c
+++ b/fs/ext4/migrate.c
@@ -327,7 +327,7 @@ static int free_ind_block(handle_t *handle, struct inode *inode, __le32 *i_data)
 }
 
 static int ext4_ext_swap_inode_data(handle_t *handle, struct inode *inode,
-                               struct inode *tmp_inode)
+                                               struct inode *tmp_inode)
 {
        int retval;
        __le32  i_data[3];
@@ -339,7 +339,7 @@ static int ext4_ext_swap_inode_data(handle_t *handle, struct inode *inode,
         * i_data field of the original inode
         */
        retval = ext4_journal_extend(handle, 1);
-       if (retval != 0) {
+       if (retval) {
                retval = ext4_journal_restart(handle, 1);
                if (retval)
                        goto err_out;
@@ -350,6 +350,18 @@ static int ext4_ext_swap_inode_data(handle_t *handle, struct inode *inode,
        i_data[2] = ei->i_data[EXT4_TIND_BLOCK];
 
        down_write(&EXT4_I(inode)->i_data_sem);
+       /*
+        * if EXT4_EXT_MIGRATE is cleared a block allocation
+        * happened after we started the migrate. We need to
+        * fail the migrate
+        */
+       if (!(EXT4_I(inode)->i_flags & EXT4_EXT_MIGRATE)) {
+               retval = -EAGAIN;
+               up_write(&EXT4_I(inode)->i_data_sem);
+               goto err_out;
+       } else
+               EXT4_I(inode)->i_flags = EXT4_I(inode)->i_flags &
+                                                       ~EXT4_EXT_MIGRATE;
        /*
         * We have the extent map build with the tmp inode.
         * Now copy the i_data across
@@ -508,6 +520,17 @@ int ext4_ext_migrate(struct inode *inode, struct file *filp,
         * switch the inode format to prevent read.
         */
        mutex_lock(&(inode->i_mutex));
+       /*
+        * Even though we take i_mutex we can still cause block allocation
+        * via mmap write to holes. If we have allocated new blocks we fail
+        * migrate.  New block allocation will clear EXT4_EXT_MIGRATE flag.
+        * The flag is updated with i_data_sem held to prevent racing with
+        * block allocation.
+        */
+       down_read((&EXT4_I(inode)->i_data_sem));
+       EXT4_I(inode)->i_flags = EXT4_I(inode)->i_flags | EXT4_EXT_MIGRATE;
+       up_read((&EXT4_I(inode)->i_data_sem));
+
        handle = ext4_journal_start(inode, 1);
 
        ei = EXT4_I(inode);
@@ -559,9 +582,15 @@ err_out:
                 * tmp_inode
                 */
                free_ext_block(handle, tmp_inode);
-       else
-               retval = ext4_ext_swap_inode_data(handle, inode,
-                                                       tmp_inode);
+       else {
+               retval = ext4_ext_swap_inode_data(handle, inode, tmp_inode);
+               if (retval)
+                       /*
+                        * if we fail to swap inode data free the extent
+                        * details of the tmp inode
+                        */
+                       free_ext_block(handle, tmp_inode);
+       }
 
        /* We mark the tmp_inode dirty via ext4_ext_tree_init. */
        if (ext4_journal_extend(handle, 1) != 0)