From 487caeef9fc08c0565e082c40a8aaf58dad92bbb Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Mon, 17 Aug 2009 22:17:20 -0400 Subject: ext4: Fix possible deadlock between ext4_truncate() and ext4_get_blocks() During truncate we are sometimes forced to start a new transaction as the amount of blocks to be journaled is both quite large and hard to predict. So far we restarted a transaction while holding i_data_sem and that violates lock ordering because i_data_sem ranks below a transaction start (and it can lead to a real deadlock with ext4_get_blocks() mapping blocks in some page while having a transaction open). We fix the problem by dropping the i_data_sem before restarting the transaction and acquire it afterwards. It's slightly subtle that this works: 1) By the time ext4_truncate() is called, all the page cache for the truncated part of the file is dropped so get_block() should not be called on it (we only have to invalidate extent cache after we reacquire i_data_sem because some extent from not-truncated part could extend also into the part we are going to truncate). 2) Writes, migrate or defrag hold i_mutex so they are stopped for all the time of the truncate. This bug has been found and analyzed by Theodore Tso . Signed-off-by: Jan Kara Signed-off-by: "Theodore Ts'o" --- fs/ext4/ext4.h | 1 + 1 file changed, 1 insertion(+) (limited to 'fs/ext4/ext4.h') diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 2e9a2036c11..fb21663ffe5 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1370,6 +1370,7 @@ extern int ext4_change_inode_journal_flag(struct inode *, int); extern int ext4_get_inode_loc(struct inode *, struct ext4_iloc *); extern int ext4_can_truncate(struct inode *inode); extern void ext4_truncate(struct inode *); +extern int ext4_truncate_restart_trans(handle_t *, struct inode *, int nblocks); extern void ext4_set_inode_flags(struct inode *); extern void ext4_get_inode_flags(struct ext4_inode_info *); extern int ext4_alloc_da_blocks(struct inode *inode); -- cgit v1.2.3-18-g5258