[PATCH v4 1/1] nilfs2: add missing blkdev_issue_flush() to nilfs_sync_fs()

[Andreas Rohner <andreas.rohner-hi6Y0CQ0nG0@public.gmane.org>]

Under normal circumstances nilfs_sync_fs() writes out the super block,
which causes a flush of the underlying block device. But this depends on
the THE_NILFS_SB_DIRTY flag, which is only set if the pointer to the
last segment crosses a segment boundary. So if only a small amount of
data is written before the call to nilfs_sync_fs(), no flush of the
block device occurs.

In the above case an additional call to blkdev_issue_flush() is needed.
To prevent unnecessary overhead, the new flag nilfs->ns_flushed_device
is introduced, which is cleared whenever new logs are written and set
whenever the block device is flushed.

Signed-off-by: Andreas Rohner <andreas.rohner-hi6Y0CQ0nG0@public.gmane.org>
---
 fs/nilfs2/file.c      | 10 +++++++++-
 fs/nilfs2/ioctl.c     | 10 +++++++++-
 fs/nilfs2/segment.c   |  4 ++++
 fs/nilfs2/super.c     | 17 +++++++++++++++++
 fs/nilfs2/the_nilfs.h |  2 ++
 5 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/fs/nilfs2/file.c b/fs/nilfs2/file.c
index 2497815..16375c2 100644
--- a/fs/nilfs2/file.c
+++ b/fs/nilfs2/file.c
@@ -56,7 +56,15 @@ int nilfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 	mutex_unlock(&inode->i_mutex);
 
 	nilfs = inode->i_sb->s_fs_info;
-	if (!err && nilfs_test_opt(nilfs, BARRIER)) {
+	if (!err && nilfs_test_opt(nilfs, BARRIER) &&
+	    !nilfs->ns_flushed_device) {
+		nilfs->ns_flushed_device = 1;
+		/*
+		 * the store to ns_flushed_device must not be reordered after
+		 * blkdev_issue_flush
+		 */
+		smp_wmb();
+
 		err = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
 		if (err != -EIO)
 			err = 0;
diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
index 422fb54..9444d5d 100644
--- a/fs/nilfs2/ioctl.c
+++ b/fs/nilfs2/ioctl.c
@@ -1022,7 +1022,15 @@ static int nilfs_ioctl_sync(struct inode *inode, struct file *filp,
 		return ret;
 
 	nilfs = inode->i_sb->s_fs_info;
-	if (nilfs_test_opt(nilfs, BARRIER)) {
+	if (nilfs_test_opt(nilfs, BARRIER) &&
+	    !nilfs->ns_flushed_device) {
+		nilfs->ns_flushed_device = 1;
+		/*
+		 * the store to ns_flushed_device must not be reordered after
+		 * blkdev_issue_flush
+		 */
+		smp_wmb();
+
 		ret = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
 		if (ret == -EIO)
 			return ret;
diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index a1a1916..379da1b 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -1997,6 +1997,10 @@ static int nilfs_segctor_do_construct(struct nilfs_sc_info *sci, int mode)
 			err = nilfs_segctor_wait(sci);
 			if (err)
 				goto failed_to_write;
+
+			if (test_bit(NILFS_SC_SUPER_ROOT, &sci->sc_flags) ||
+			    mode == SC_LSEG_DSYNC)
+				nilfs->ns_flushed_device = 0;
 		}
 	} while (sci->sc_stage.scnt != NILFS_ST_DONE);
 
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index 228f5bd..33aafbd 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -310,6 +310,9 @@ int nilfs_commit_super(struct super_block *sb, int flag)
 					    nilfs->ns_sbsize));
 	}
 	clear_nilfs_sb_dirty(nilfs);
+	nilfs->ns_flushed_device = 1;
+	/* make sure store to ns_flushed_device cannot be reordered */
+	smp_wmb();
 	return nilfs_sync_super(sb, flag);
 }
 
@@ -514,6 +517,20 @@ static int nilfs_sync_fs(struct super_block *sb, int wait)
 	}
 	up_write(&nilfs->ns_sem);
 
+	if (wait && !err && nilfs_test_opt(nilfs, BARRIER) &&
+	    !nilfs->ns_flushed_device) {
+		nilfs->ns_flushed_device = 1;
+		/*
+		 * the store to ns_flushed_device must not be reordered after
+		 * blkdev_issue_flush
+		 */
+		smp_wmb();
+
+		err = blkdev_issue_flush(sb->s_bdev, GFP_KERNEL, NULL);
+		if (err != -EIO)
+			err = 0;
+	}
+
 	return err;
 }
 
diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
index d01ead1..dabb02c 100644
--- a/fs/nilfs2/the_nilfs.h
+++ b/fs/nilfs2/the_nilfs.h
@@ -45,6 +45,7 @@ enum {
 
 /**
  * struct the_nilfs - struct to supervise multiple nilfs mount points
+ * @ns_flushed_device: flag indicating if all volatile data was flushed
  * @ns_flags: flags
  * @ns_bdev: block device
  * @ns_sem: semaphore for shared states
@@ -103,6 +104,7 @@ enum {
  */
 struct the_nilfs {
 	unsigned long		ns_flags;
+	int			ns_flushed_device;
 
 	struct block_device    *ns_bdev;
 	struct rw_semaphore	ns_sem;
-- 
2.1.0

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