[PATCH 3/7] ext4: serialize dio nolocked reads with defrag workers V2

[Dmitry Monakhov <dmonakhov@openvz.org>]

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 <dmonakhov@openvz.org>
---
 fs/ext4/ext4.h        |    3 +++
 fs/ext4/indirect.c    |   23 +++++++++++++++++++++++
 fs/ext4/inode.c       |    4 ++++
 fs/ext4/move_extent.c |    5 +++++
 4 files changed, 35 insertions(+), 0 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index be976ca..0377d2b 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1348,6 +1348,8 @@ 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)				\
@@ -2015,6 +2017,7 @@ extern void ext4_da_update_reserve_space(struct inode *inode,
 /* indirect.c */
 extern int ext4_ind_map_blocks(handle_t *handle, struct inode *inode,
 				struct ext4_map_blocks *map, int flags);
+extern void ext4_inode_dio_wait(struct inode *inode, int resume);
 extern ssize_t ext4_ind_direct_IO(int rw, struct kiocb *iocb,
 				const struct iovec *iov, loff_t offset,
 				unsigned long nr_segs);
diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index 61f13e5..3714413 100644
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c
@@ -760,6 +760,19 @@ out:
 	return err;
 }
 
+/* Wait for existing dio workers
+ * Disable DIO read nolock optimization, so new dioreaders will
+ * be forced to grab i_mutex
+*/
+void ext4_inode_dio_wait(struct inode *inode, int resume_readers)
+{
+	ext4_set_inode_state(inode, EXT4_STATE_DIOREAD_LOCK);
+	smp_mb();
+	inode_dio_wait(inode);
+	if (resume_readers)
+		ext4_set_inode_state(inode, EXT4_STATE_DIOREAD_LOCK);
+}
+
 /*
  * O_DIRECT for ext3 (or indirect map) based files
  *
@@ -810,10 +823,20 @@ retry:
 		if (unlikely(!list_empty(&ei->i_completed_io_list)))
 			ext4_flush_completed_IO(inode);
 
+		/* Nolock dioread optimization may be dynamically disabled.
+		 * 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))) {
+			inode_dio_done(inode);
+			goto retry;
+		}
 		ret = __blockdev_direct_IO(rw, iocb, inode,
 				 inode->i_sb->s_bdev, iov,
 				 offset, nr_segs,
 				 ext4_get_block, NULL, NULL, 0);
+		inode_dio_done(inode);
 	} else {
 		ret = blockdev_direct_IO(rw, iocb, inode, iov,
 				 offset, nr_segs, ext4_get_block);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 762b955..ffb4a27 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4720,6 +4720,9 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
 			return err;
 	}
 
+	/* Wait for all existing dio workers */
+	ext4_inode_dio_wait(inode, 0);
+
 	jbd2_journal_lock_updates(journal);
 
 	/*
@@ -4739,6 +4742,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
 	ext4_set_aops(inode);
 
 	jbd2_journal_unlock_updates(journal);
+	ext4_clear_inode_state(inode, EXT4_STATE_DIOREAD_LOCK);
 
 	/* Finally we can mark the inode as dirty. */
 
diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index c5826c6..aea0e7a 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -1214,6 +1214,9 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp,
 	if (ret1 < 0)
 		return ret1;
 
+	/* Wait for all existing dio workers */
+	ext4_inode_dio_wait(orig_inode, 0);
+	ext4_inode_dio_wait(donor_inode, 0);
 	/* Protect extent tree against block allocations via delalloc */
 	double_down_write_data_sem(orig_inode, donor_inode);
 	/* Check the filesystem environment whether move_extent can be done */
@@ -1412,6 +1415,8 @@ out:
 		kfree(holecheck_path);
 	}
 	double_up_write_data_sem(orig_inode, donor_inode);
+	ext4_clear_inode_state(orig_inode, EXT4_STATE_DIOREAD_LOCK);
+	ext4_clear_inode_state(donor_inode, EXT4_STATE_DIOREAD_LOCK);
 	ret2 = mext_inode_double_unlock(orig_inode, donor_inode);
 
 	if (ret1)
-- 
1.7.7.6