[PATCH v9 20/22] ext4: Avoid lock inversion between i_mmap_mutex and transaction start

[Matthew Wilcox]

From: Jan Kara <jack@xxxxxxx>

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@xxxxxxx>
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@xxxxxxxxx>
---
 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 8a06473..494a864 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);
 out_dio:
-- 
2.0.1

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