ext3: Fix lock inversion in ext3_symlink()

ext3_symlink() cannot call __page_symlink() with transaction open.
__page_symlink() calls ext3_write_begin() which gets page lock which ranks
above transaction start (thus lock ordering is violated) and and also
ext3_write_begin() waits for a transaction commit when we run out of space
which never happens if we hold transaction open.

Fix the problem by stopping a transaction before calling __page_symlink()
(we have to be careful and put inode to orphan list so that it gets deleted
in case of crash) and starting another one after __page_symlink() returns
for addition of symlink into a directory.

Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 56 insertions, 11 deletions

diff --git a/fs/ext3/namei.c b/fs/ext3/namei.c
index 32f3b869585..f6ce3e79d31 100644
--- a/fs/ext3/namei.c
+++ b/fs/ext3/namei.c
@@ -2189,6 +2189,7 @@ static int ext3_symlink (struct inode * dir,
         handle_t *handle;
         struct inode * inode;
         int l, err, retries = 0;
+        int credits;
 
         l = strlen(symname)+1;
         if (l > dir->i_sb->s_blocksize)
@@ -2196,10 +2197,26 @@ static int ext3_symlink (struct inode * dir,
 
         dquot_initialize(dir);
 
+        if (l > EXT3_N_BLOCKS * 4) {
+                /*
+                 * For non-fast symlinks, we just allocate inode and put it on
+                 * orphan list in the first transaction => we need bitmap,
+                 * group descriptor, sb, inode block, quota blocks.
+                 */
+                credits = 4 + EXT3_MAXQUOTAS_INIT_BLOCKS(dir->i_sb);
+        } else {
+                /*
+                 * Fast symlink. We have to add entry to directory
+                 * (EXT3_DATA_TRANS_BLOCKS + EXT3_INDEX_EXTRA_TRANS_BLOCKS),
+                 * allocate new inode (bitmap, group descriptor, inode block,
+                 * quota blocks, sb is already counted in previous macros).
+                 */
+                credits = EXT3_DATA_TRANS_BLOCKS(dir->i_sb) +
+                          EXT3_INDEX_EXTRA_TRANS_BLOCKS + 3 +
+                          EXT3_MAXQUOTAS_INIT_BLOCKS(dir->i_sb);
+        }
 retry:
-        handle = ext3_journal_start(dir, EXT3_DATA_TRANS_BLOCKS(dir->i_sb) +
-                                        EXT3_INDEX_EXTRA_TRANS_BLOCKS + 5 +
-                                        EXT3_MAXQUOTAS_INIT_BLOCKS(dir->i_sb));
+        handle = ext3_journal_start(dir, credits);
         if (IS_ERR(handle))
                 return PTR_ERR(handle);
 
@@ -2211,21 +2228,45 @@ retry:
         if (IS_ERR(inode))
                 goto out_stop;
 
-        if (l > sizeof (EXT3_I(inode)->i_data)) {
+        if (l > EXT3_N_BLOCKS * 4) {
                 inode->i_op = &ext3_symlink_inode_operations;
                 ext3_set_aops(inode);
                 /*
-                 * page_symlink() calls into ext3_prepare/commit_write.
-                 * We have a transaction open.  All is sweetness.  It also sets
-                 * i_size in generic_commit_write().
+                 * We cannot call page_symlink() with transaction started
+                 * because it calls into ext3_write_begin() which acquires page
+                 * lock which ranks below transaction start (and it can also
+                 * wait for journal commit if we are running out of space). So
+                 * we have to stop transaction now and restart it when symlink
+                 * contents is written. 
+                 *
+                 * To keep fs consistent in case of crash, we have to put inode
+                 * to orphan list in the mean time.
                  */
+                drop_nlink(inode);
+                err = ext3_orphan_add(handle, inode);
+                ext3_journal_stop(handle);
+                if (err)
+                        goto err_drop_inode;
                 err = __page_symlink(inode, symname, l, 1);
+                if (err)
+                        goto err_drop_inode;
+                /*
+                 * Now inode is being linked into dir (EXT3_DATA_TRANS_BLOCKS
+                 * + EXT3_INDEX_EXTRA_TRANS_BLOCKS), inode is also modified
+                 */
+                handle = ext3_journal_start(dir,
+                                EXT3_DATA_TRANS_BLOCKS(dir->i_sb) +
+                                EXT3_INDEX_EXTRA_TRANS_BLOCKS + 1);
+                if (IS_ERR(handle)) {
+                        err = PTR_ERR(handle);
+                        goto err_drop_inode;
+                }
+                inc_nlink(inode);
+                err = ext3_orphan_del(handle, inode);
                 if (err) {
+                        ext3_journal_stop(handle);
                         drop_nlink(inode);
-                        unlock_new_inode(inode);
-                        ext3_mark_inode_dirty(handle, inode);
-                        iput (inode);
-                        goto out_stop;
+                        goto err_drop_inode;
                 }
         } else {
                 inode->i_op = &ext3_fast_symlink_inode_operations;
@@ -2239,6 +2280,10 @@ out_stop:
         if (err == -ENOSPC && ext3_should_retry_alloc(dir->i_sb, &retries))
                 goto retry;
         return err;
+err_drop_inode:
+        unlock_new_inode(inode);
+        iput (inode);
+        return err;
 }
 
 static int ext3_link (struct dentry * old_dentry,