ext4: Fix circular locking dependency with migrate and rm.

In order to prevent a circular locking dependency when an unlink
operation is racing with an ext4 migration, we delay taking i_data_sem
until just before switch the inode format, and use i_mutex to prevent
writes and truncates during the first part of the migration operation.

Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 74 insertions, 43 deletions

diff --git a/fs/ext4/migrate.c b/fs/ext4/migrate.c
index 9ee1f7cfb2c5..8c6c685b9d22 100644
--- a/fs/ext4/migrate.c
+++ b/fs/ext4/migrate.c
@@ -61,10 +61,9 @@ static int finish_range(handle_t *handle, struct inode *inode,
                 retval = ext4_journal_restart(handle, needed);
                 if (retval)
                         goto err_out;
-        }
-        if (needed) {
+        } else if (needed) {
                 retval = ext4_journal_extend(handle, needed);
-                if (retval != 0) {
+                if (retval) {
                         /*
                          * IF not able to extend the journal restart the journal
                          */
@@ -220,6 +219,26 @@ static int update_tind_extent_range(handle_t *handle, struct inode *inode,
 
 }
 
+static int extend_credit_for_blkdel(handle_t *handle, struct inode *inode)
+{
+        int retval = 0, needed;
+
+        if (handle->h_buffer_credits > EXT4_RESERVE_TRANS_BLOCKS)
+                return 0;
+        /*
+         * We are freeing a blocks. During this we touch
+         * superblock, group descriptor and block bitmap.
+         * So allocate a credit of 3. We may update
+         * quota (user and group).
+         */
+        needed = 3 + 2*EXT4_QUOTA_TRANS_BLOCKS(inode->i_sb);
+
+        if (ext4_journal_extend(handle, needed) != 0)
+                retval = ext4_journal_restart(handle, needed);
+
+        return retval;
+}
+
 static int free_dind_blocks(handle_t *handle,
                                 struct inode *inode, __le32 i_data)
 {
@@ -234,11 +253,14 @@ static int free_dind_blocks(handle_t *handle,
 
         tmp_idata = (__le32 *)bh->b_data;
         for (i = 0; i < max_entries; i++) {
-                if (tmp_idata[i])
+                if (tmp_idata[i]) {
+                        extend_credit_for_blkdel(handle, inode);
                         ext4_free_blocks(handle, inode,
                                         le32_to_cpu(tmp_idata[i]), 1, 1);
+                }
         }
         put_bh(bh);
+        extend_credit_for_blkdel(handle, inode);
         ext4_free_blocks(handle, inode, le32_to_cpu(i_data), 1, 1);
         return 0;
 }
@@ -267,29 +289,32 @@ static int free_tind_blocks(handle_t *handle,
                 }
         }
         put_bh(bh);
+        extend_credit_for_blkdel(handle, inode);
         ext4_free_blocks(handle, inode, le32_to_cpu(i_data), 1, 1);
         return 0;
 }
 
-static int free_ind_block(handle_t *handle, struct inode *inode)
+static int free_ind_block(handle_t *handle, struct inode *inode, __le32 *i_data)
 {
         int retval;
-        struct ext4_inode_info *ei = EXT4_I(inode);
 
-        if (ei->i_data[EXT4_IND_BLOCK])
+        /* ei->i_data[EXT4_IND_BLOCK] */
+        if (i_data[0]) {
+                extend_credit_for_blkdel(handle, inode);
                 ext4_free_blocks(handle, inode,
-                                le32_to_cpu(ei->i_data[EXT4_IND_BLOCK]), 1, 1);
+                                le32_to_cpu(i_data[0]), 1, 1);
+        }
 
-        if (ei->i_data[EXT4_DIND_BLOCK]) {
-                retval = free_dind_blocks(handle, inode,
-                                                ei->i_data[EXT4_DIND_BLOCK]);
+        /* ei->i_data[EXT4_DIND_BLOCK] */
+        if (i_data[1]) {
+                retval = free_dind_blocks(handle, inode, i_data[1]);
                 if (retval)
                         return retval;
         }
 
-        if (ei->i_data[EXT4_TIND_BLOCK]) {
-                retval = free_tind_blocks(handle, inode,
-                                                ei->i_data[EXT4_TIND_BLOCK]);
+        /* ei->i_data[EXT4_TIND_BLOCK] */
+        if (i_data[2]) {
+                retval = free_tind_blocks(handle, inode, i_data[2]);
                 if (retval)
                         return retval;
         }
@@ -297,15 +322,13 @@ static int free_ind_block(handle_t *handle, struct inode *inode)
 }
 
 static int ext4_ext_swap_inode_data(handle_t *handle, struct inode *inode,
-                                struct inode *tmp_inode, int retval)
+                                struct inode *tmp_inode)
 {
+        int retval;
+        __le32  i_data[3];
         struct ext4_inode_info *ei = EXT4_I(inode);
         struct ext4_inode_info *tmp_ei = EXT4_I(tmp_inode);
 
-        retval = free_ind_block(handle, inode);
-        if (retval)
-                goto err_out;
-
         /*
          * One credit accounted for writing the
          * i_data field of the original inode
@@ -317,6 +340,11 @@ static int ext4_ext_swap_inode_data(handle_t *handle, struct inode *inode,
                         goto err_out;
         }
 
+        i_data[0] = ei->i_data[EXT4_IND_BLOCK];
+        i_data[1] = ei->i_data[EXT4_DIND_BLOCK];
+        i_data[2] = ei->i_data[EXT4_TIND_BLOCK];
+
+        down_write(&EXT4_I(inode)->i_data_sem);
         /*
          * We have the extent map build with the tmp inode.
          * Now copy the i_data across
@@ -336,8 +364,15 @@ static int ext4_ext_swap_inode_data(handle_t *handle, struct inode *inode,
         spin_lock(&inode->i_lock);
         inode->i_blocks += tmp_inode->i_blocks;
         spin_unlock(&inode->i_lock);
+        up_write(&EXT4_I(inode)->i_data_sem);
 
+        /*
+         * We mark the inode dirty after, because we decrement the
+         * i_blocks when freeing the indirect meta-data blocks
+         */
+        retval = free_ind_block(handle, inode, i_data);
         ext4_mark_inode_dirty(handle, inode);
+
 err_out:
         return retval;
 }
@@ -365,6 +400,7 @@ static int free_ext_idx(handle_t *handle, struct inode *inode,
                 }
         }
         put_bh(bh);
+        extend_credit_for_blkdel(handle, inode);
         ext4_free_blocks(handle, inode, block, 1, 1);
         return retval;
 }
@@ -420,7 +456,6 @@ int ext4_ext_migrate(struct inode *inode, struct file *filp,
                  */
                 return retval;
 
-        down_write(&EXT4_I(inode)->i_data_sem);
         handle = ext4_journal_start(inode,
                                         EXT4_DATA_TRANS_BLOCKS(inode->i_sb) +
                                         EXT4_INDEX_EXTRA_TRANS_BLOCKS + 3 +
@@ -454,13 +489,6 @@ int ext4_ext_migrate(struct inode *inode, struct file *filp,
         ext4_orphan_add(handle, tmp_inode);
         ext4_journal_stop(handle);
 
-        ei = EXT4_I(inode);
-        i_data = ei->i_data;
-        memset(&lb, 0, sizeof(lb));
-
-        /* 32 bit block address 4 bytes */
-        max_entries = inode->i_sb->s_blocksize >> 2;
-
         /*
          * start with one credit accounted for
          * superblock modification.
@@ -469,7 +497,20 @@ int ext4_ext_migrate(struct inode *inode, struct file *filp,
          * trascation that created the inode. Later as and
          * when we add extents we extent the journal
          */
+        /*
+         * inode_mutex prevent write and truncate on the file. Read still goes
+         * through. We take i_data_sem in ext4_ext_swap_inode_data before we
+         * switch the inode format to prevent read.
+         */
+        mutex_lock(&(inode->i_mutex));
         handle = ext4_journal_start(inode, 1);
+
+        ei = EXT4_I(inode);
+        i_data = ei->i_data;
+        memset(&lb, 0, sizeof(lb));
+
+        /* 32 bit block address 4 bytes */
+        max_entries = inode->i_sb->s_blocksize >> 2;
         for (i = 0; i < EXT4_NDIR_BLOCKS; i++, blk_count++) {
                 if (i_data[i]) {
                         retval = update_extent_range(handle, tmp_inode,
@@ -507,19 +548,6 @@ int ext4_ext_migrate(struct inode *inode, struct file *filp,
          */
         retval = finish_range(handle, tmp_inode, &lb);
 err_out:
-        /*
-         * We are either freeing extent information or indirect
-         * blocks. During this we touch superblock, group descriptor
-         * and block bitmap. Later we mark the tmp_inode dirty
-         * via ext4_ext_tree_init. So allocate a credit of 4
-         * We may update quota (user and group).
-         *
-         * FIXME!! we may be touching bitmaps in different block groups.
-         */
-        if (ext4_journal_extend(handle,
-                        4 + 2*EXT4_QUOTA_TRANS_BLOCKS(inode->i_sb)) != 0)
-                ext4_journal_restart(handle,
-                                4 + 2*EXT4_QUOTA_TRANS_BLOCKS(inode->i_sb));
         if (retval)
                 /*
                  * Failure case delete the extent information with the
@@ -528,7 +556,11 @@ err_out:
                 free_ext_block(handle, tmp_inode);
         else
                 retval = ext4_ext_swap_inode_data(handle, inode,
-                                                        tmp_inode, retval);
+                                                        tmp_inode);
+
+        /* We mark the tmp_inode dirty via ext4_ext_tree_init. */
+        if (ext4_journal_extend(handle, 1) != 0)
+                ext4_journal_restart(handle, 1);
 
         /*
          * Mark the tmp_inode as of size zero
@@ -556,8 +588,7 @@ err_out:
         tmp_inode->i_nlink = 0;
 
         ext4_journal_stop(handle);
-
-        up_write(&EXT4_I(inode)->i_data_sem);
+        mutex_unlock(&(inode->i_mutex));
 
         if (tmp_inode)
                 iput(tmp_inode);