[PATCH] ext4: Avoid lock inversion between i_mmap_mutex and transaction start

Jan Kara
2014-10-10T14:24:09Z

When DAX is enabled, it uses i_mmap_mutex as a protection against
truncate during page fault. This inevitably forces i_mmap_mutex to rank
outside of a transaction start and thus we have to avoid calling
pagecache purging operations when transaction is started.

Signed-off-by: Jan Kara <jack@suse.cz>
---
fs/ext4/inode.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 8a064734e6eb..494a8645d63e 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3631,13 +3631,19 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
if (IS_SYNC(inode))
ext4_handle_sync(handle);

- /* Now release the pages again to reduce race window */
+ inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
+ ext4_mark_inode_dirty(handle, inode);
+ ext4_journal_stop(handle);
+
+ /*
+ * Now release the pages again to reduce race window. This has to happen
+ * outside of a transaction to avoid lock inversion on i_mmap_mutex
+ * when DAX is enabled.
+ */
if (last_block_offset > first_block_offset)
truncate_pagecache_range(inode, first_block_offset,
last_block_offset);
-
- inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
- ext4_mark_inode_dirty(handle, inode);
+ goto out_dio;
out_stop:
ext4_journal_stop(handle);