Re: [PATCH 05/10] ext4: serialize dio nonlocked reads with defrag workers V3

Inode's block defrag and ext4_change_inode_journal_flag() may
affect nonlocked DIO reads result, so proper synchronization
required.

- Add missed inode_dio_wait() calls where appropriate
- Check inode state under extra i_dio_count reference.


Changes from V1:
- add missed memory bariers
- move DIOREAD_LOCK state check out from generic should_dioread_nolock
  otherwise it will affect existing DIO readers.

Signed-off-by: Dmitry Monakhov <redacted>
---
 fs/ext4/ext4.h        |   17 +++++++++++++++++
 fs/ext4/indirect.c    |   13 +++++++++++++
 fs/ext4/inode.c       |    5 +++++
 fs/ext4/move_extent.c |    8 ++++++++
 4 files changed, 43 insertions(+), 0 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index cc423cf..fccd263 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h

@@ -1350,6 +1350,8 @@ enum {
 	EXT4_STATE_DIO_UNWRITTEN,	/* need convert on dio done*/
 	EXT4_STATE_NEWENTRY,		/* File just added to dir */
 	EXT4_STATE_DELALLOC_RESERVED,	/* blks already reserved for delalloc */
+	EXT4_STATE_DIOREAD_LOCK,	/* Disable support for dio read
+					   nolocking */
 };
 
 #define EXT4_INODE_BIT_FNS(name, field, offset)				\

@@ -2462,6 +2464,21 @@ static inline void set_bitmap_uptodate(struct buffer_head *bh)
 	set_bit(BH_BITMAP_UPTODATE, &(bh)->b_state);
 }
 
+/*
+ * Disable DIO read nolock optimization, so new dioreaders will be forced
+ * to grab i_mutex
+ */
+static inline void ext4_inode_block_unlocked_dio(struct inode *inode)
+{
+	ext4_set_inode_state(inode, EXT4_STATE_DIOREAD_LOCK);
+	smp_mb();
+}
+static inline void ext4_inode_resume_unlocked_dio(struct inode *inode)
+{
+	smp_mb();
+	ext4_clear_inode_state(inode, EXT4_STATE_DIOREAD_LOCK);
+}
+
 #define in_range(b, first, len)	((b) >= (first) && (b) <= (first) + (len) - 1)
 
 /* For ioend & aio unwritten conversion wait queues */

diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index 251e35f..ec38f81 100644
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c

@@ -810,10 +810,23 @@ retry:
 		if (unlikely(!list_empty(&ei->i_completed_io_list)))
 			ext4_unwritten_wait(inode);
 
+		/*
+		 * Nolock dioread optimization may be dynamically disabled
+		 * via ext4_inode_block_unlocked_dio(). Check inode's state
+		 * while holding extra i_dio_count ref.
+		 */
+		atomic_inc(&inode->i_dio_count);
+		smp_mb();
+		if (!unlikely(ext4_test_inode_state(inode,
+						    EXT4_STATE_DIOREAD_LOCK))) {