Commit df5e6223 authored by Jan Kara's avatar Jan Kara Committed by Theodore Ts'o
Browse files

ext4: fix deadlock in ext4_symlink() in ENOSPC conditions 



ext4_symlink() cannot call __page_symlink() with transaction open.
__page_symlink() calls ext4_write_begin() which can wait for
transaction commit if we are running out of space thus causing a
deadlock. Also error recovery in ext4_truncate_failed_write() does not
count with the transaction being already started (although I'm not
aware of any particular deadlock here).

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: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 7ad8e4e6

fs/ext4/namei.c

+55 −11
Original line number Diff line number Diff line
@@ -2250,6 +2250,7 @@ static int ext4_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)
@@ -2257,10 +2258,26 @@ static int ext4_symlink(struct inode *dir, 


	dquot_initialize(dir);



	if (l > EXT4_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 + EXT4_MAXQUOTAS_INIT_BLOCKS(dir->i_sb);

	} else {

		/*

		 * Fast symlink. We have to add entry to directory

		 * (EXT4_DATA_TRANS_BLOCKS + EXT4_INDEX_EXTRA_TRANS_BLOCKS),

		 * allocate new inode (bitmap, group descriptor, inode block,

		 * quota blocks, sb is already counted in previous macros).

		 */

		credits = EXT4_DATA_TRANS_BLOCKS(dir->i_sb) +

			  EXT4_INDEX_EXTRA_TRANS_BLOCKS + 3 +

			  EXT4_MAXQUOTAS_INIT_BLOCKS(dir->i_sb);

	}

retry:

	handle = ext4_journal_start(dir, EXT4_DATA_TRANS_BLOCKS(dir->i_sb) +

					EXT4_INDEX_EXTRA_TRANS_BLOCKS + 5 +

					EXT4_MAXQUOTAS_INIT_BLOCKS(dir->i_sb));

	handle = ext4_journal_start(dir, credits);

	if (IS_ERR(handle))

		return PTR_ERR(handle);
@@ -2273,21 +2290,44 @@ retry: 
	if (IS_ERR(inode))

		goto out_stop;



	if (l > sizeof(EXT4_I(inode)->i_data)) {

	if (l > EXT4_N_BLOCKS * 4) {

		inode->i_op = &ext4_symlink_inode_operations;

		ext4_set_aops(inode);

		/*

		 * page_symlink() calls into ext4_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 ext4_write_begin() which can wait

		 * for transaction commit if we are running out of space

		 * and thus we deadlock. 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 = ext4_orphan_add(handle, inode);

		ext4_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 (EXT4_DATA_TRANS_BLOCKS

		 * + EXT4_INDEX_EXTRA_TRANS_BLOCKS), inode is also modified

		 */

		handle = ext4_journal_start(dir,

				EXT4_DATA_TRANS_BLOCKS(dir->i_sb) +

				EXT4_INDEX_EXTRA_TRANS_BLOCKS + 1);

		if (IS_ERR(handle)) {

			err = PTR_ERR(handle);

			goto err_drop_inode;

		}

		inc_nlink(inode);

		err = ext4_orphan_del(handle, inode);

		if (err) {

			ext4_journal_stop(handle);

			clear_nlink(inode);

			unlock_new_inode(inode);

			ext4_mark_inode_dirty(handle, inode);

			iput(inode);

			goto out_stop;

			goto err_drop_inode;

		}

	} else {

		/* clear the extent format for fast symlink */
@@ -2303,6 +2343,10 @@ out_stop: 
	if (err == -ENOSPC && ext4_should_retry_alloc(dir->i_sb, &retries))

		goto retry;

	return err;

err_drop_inode:

	unlock_new_inode(inode);

	iput(inode);

	return err;

}



static int ext4_link(struct dentry *old_dentry,

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