lazytime fix and cleanups

index acfb55834af23..c41cb887eb7d3 100644
@@ -1474,21 +1474,25 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 	}
 
 	/*
-	 * Some filesystems may redirty the inode during the writeback
-	 * due to delalloc, clear dirty metadata flags right before
-	 * write_inode()
+	 * If the inode has dirty timestamps and we need to write them, call
+	 * mark_inode_dirty_sync() to notify the filesystem about it and to
+	 * change I_DIRTY_TIME into I_DIRTY_SYNC.
 	 */
-	spin_lock(&inode->i_lock);
-
-	dirty = inode->i_state & I_DIRTY;
 	if ((inode->i_state & I_DIRTY_TIME) &&
-	    ((dirty & I_DIRTY_INODE) ||
-	     wbc->sync_mode == WB_SYNC_ALL || wbc->for_sync ||
+	    (wbc->sync_mode == WB_SYNC_ALL || wbc->for_sync ||
 	     time_after(jiffies, inode->dirtied_time_when +
 			dirtytime_expire_interval * HZ))) {
-		dirty |= I_DIRTY_TIME;
 		trace_writeback_lazytime(inode);
+		mark_inode_dirty_sync(inode);
 	}
+
+	/*
+	 * Some filesystems may redirty the inode during the writeback
+	 * due to delalloc, clear dirty metadata flags right before
+	 * write_inode()
+	 */
+	spin_lock(&inode->i_lock);
+	dirty = inode->i_state & I_DIRTY;
 	inode->i_state &= ~dirty;
 
 	/*

@@ -1509,8 +1513,6 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 
 	spin_unlock(&inode->i_lock);
 
-	if (dirty & I_DIRTY_TIME)
-		mark_inode_dirty_sync(inode);
 	/* Don't write the inode if only I_DIRTY_PAGES was set */
 	if (dirty & ~I_DIRTY_PAGES) {
 		int err = write_inode(inode, wbc);

index fd47deea7c176..45a0303b2aeb6 100644
@@ -2084,8 +2084,8 @@ static inline void kiocb_clone(struct kiocb *kiocb, struct kiocb *kiocb_src,
 /*
  * Inode state bits.  Protected by inode->i_lock
  *
- * Three bits determine the dirty state of the inode, I_DIRTY_SYNC,
- * I_DIRTY_DATASYNC and I_DIRTY_PAGES.
+ * Four bits determine the dirty state of the inode: I_DIRTY_SYNC,
+ * I_DIRTY_DATASYNC, I_DIRTY_PAGES, and I_DIRTY_TIME.
  *
  * Four bits define the lifetime of an inode.  Initially, inodes are I_NEW,
  * until that flag is cleared.  I_WILL_FREE, I_FREEING and I_CLEAR are set at

@@ -2094,12 +2094,20 @@ static inline void kiocb_clone(struct kiocb *kiocb, struct kiocb *kiocb_src,
  * Two bits are used for locking and completion notification, I_NEW and I_SYNC.
  *
  * I_DIRTY_SYNC		Inode is dirty, but doesn't have to be written on
- *			fdatasync().  i_atime is the usual cause.
- * I_DIRTY_DATASYNC	Data-related inode changes pending. We keep track of
+ *			fdatasync() (unless I_DIRTY_DATASYNC is also set).
+ *			Timestamp updates are the usual cause.
+ * I_DIRTY_DATASYNC	Data-related inode changes pending.  We keep track of
  *			these changes separately from I_DIRTY_SYNC so that we
  *			don't have to write inode on fdatasync() when only
- *			mtime has changed in it.
+ *			e.g. the timestamps have changed.
  * I_DIRTY_PAGES	Inode has dirty pages.  Inode itself may be clean.
+ * I_DIRTY_TIME		The inode itself only has dirty timestamps, and the
+ *			lazytime mount option is enabled.  We keep track of this
+ *			separately from I_DIRTY_SYNC in order to implement
+ *			lazytime.  This gets cleared if I_DIRTY_INODE
+ *			(I_DIRTY_SYNC and/or I_DIRTY_DATASYNC) gets set.  I.e.
+ *			either I_DIRTY_TIME *or* I_DIRTY_INODE can be set in
+ *			i_state, but not both.  I_DIRTY_PAGES may still be set.
  * I_NEW		Serves as both a mutex and completion notification.
  *			New inodes set I_NEW.  If two processes both create
  *			the same inode, one of them will release its inode and

index 6442d97d9a4ab..d0fa43d8e9d5c 100644
@@ -1743,24 +1743,26 @@ static int relatime_need_update(struct vfsmount *mnt, struct inode *inode,
 
 int generic_update_time(struct inode *inode, struct timespec64 *time, int flags)
 {
-	int iflags = I_DIRTY_TIME;
-	bool dirty = false;
-
-	if (flags & S_ATIME)
-		inode->i_atime = *time;
-	if (flags & S_VERSION)
-		dirty = inode_maybe_inc_iversion(inode, false);
-	if (flags & S_CTIME)
-		inode->i_ctime = *time;
-	if (flags & S_MTIME)
-		inode->i_mtime = *time;
-	if ((flags & (S_ATIME | S_CTIME | S_MTIME)) &&
-	    !(inode->i_sb->s_flags & SB_LAZYTIME))
-		dirty = true;
-
-	if (dirty)
-		iflags |= I_DIRTY_SYNC;
-	__mark_inode_dirty(inode, iflags);
+	int dirty_flags = 0;
+
+	if (flags & (S_ATIME | S_CTIME | S_MTIME)) {
+		if (flags & S_ATIME)
+			inode->i_atime = *time;
+		if (flags & S_CTIME)
+			inode->i_ctime = *time;
+		if (flags & S_MTIME)
+			inode->i_mtime = *time;
+
+		if (inode->i_sb->s_flags & SB_LAZYTIME)
+			dirty_flags |= I_DIRTY_TIME;
+		else
+			dirty_flags |= I_DIRTY_SYNC;
+	}
+
+	if ((flags & S_VERSION) && inode_maybe_inc_iversion(inode, false))
+		dirty_flags |= I_DIRTY_SYNC;
+
+	__mark_inode_dirty(inode, dirty_flags);
 	return 0;
 }
 EXPORT_SYMBOL(generic_update_time);

index f1b2a1fc2a6a4..18a50a46b57f8 100644
@@ -329,22 +329,23 @@ EXPORT_SYMBOL_GPL(fat_truncate_time);
 
 int fat_update_time(struct inode *inode, struct timespec64 *now, int flags)
 {
-	int iflags = I_DIRTY_TIME;
-	bool dirty = false;
+	int dirty_flags = 0;
 
 	if (inode->i_ino == MSDOS_ROOT_INO)
 		return 0;
 
-	fat_truncate_time(inode, now, flags);
-	if (flags & S_VERSION)
-		dirty = inode_maybe_inc_iversion(inode, false);
-	if ((flags & (S_ATIME | S_CTIME | S_MTIME)) &&
-	    !(inode->i_sb->s_flags & SB_LAZYTIME))
-		dirty = true;
+	if (flags & (S_ATIME | S_CTIME | S_MTIME)) {
+		fat_truncate_time(inode, now, flags);
+		if (inode->i_sb->s_flags & SB_LAZYTIME)
+			dirty_flags |= I_DIRTY_TIME;
+		else
+			dirty_flags |= I_DIRTY_SYNC;
+	}
+
+	if ((flags & S_VERSION) && inode_maybe_inc_iversion(inode, false))
+		dirty_flags |= I_DIRTY_SYNC;
 
-	if (dirty)
-		iflags |= I_DIRTY_SYNC;
-	__mark_inode_dirty(inode, iflags);
+	__mark_inode_dirty(inode, dirty_flags);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(fat_update_time);

index 27946882d4ce4..4cc6c7834312f 100644
@@ -5933,26 +5933,16 @@ int __ext4_mark_inode_dirty(handle_t *handle, struct inode *inode,
  * If the inode is marked synchronous, we don't honour that here - doing
  * so would cause a commit on atime updates, which we don't bother doing.
  * We handle synchronous inodes at the highest possible level.
- *
- * If only the I_DIRTY_TIME flag is set, we can skip everything.  If
- * I_DIRTY_TIME and I_DIRTY_SYNC is set, the only inode fields we need
- * to copy into the on-disk inode structure are the timestamp files.
  */
 void ext4_dirty_inode(struct inode *inode, int flags)
 {
 	handle_t *handle;
 
-	if (flags == I_DIRTY_TIME)
-		return;
 	handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
 	if (IS_ERR(handle))
-		goto out;
-
+		return;
 	ext4_mark_inode_dirty(handle, inode);
-
 	ext4_journal_stop(handle);
-out:
-	return;
 }
 
 int ext4_change_inode_journal_flag(struct inode *inode, int val)

index b4a07fe62d1a5..cc98dc49f4a26 100644
@@ -1196,9 +1196,6 @@ static void f2fs_dirty_inode(struct inode *inode, int flags)
 			inode->i_ino == F2FS_META_INO(sbi))
 		return;
 
-	if (flags == I_DIRTY_TIME)
-		return;
-
 	if (is_inode_flag_set(inode, FI_AUTO_RECOVER))
 		clear_inode_flag(inode, FI_AUTO_RECOVER);
 

index c41cb887eb7d3..b7616bbd55336 100644
@@ -2255,16 +2255,16 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 	 * Don't do this for I_DIRTY_PAGES - that doesn't actually
 	 * dirty the inode itself
 	 */
-	if (flags & (I_DIRTY_INODE | I_DIRTY_TIME)) {
+	if (flags & I_DIRTY_INODE) {
 		trace_writeback_dirty_inode_start(inode, flags);
 
 		if (sb->s_op->dirty_inode)
 			sb->s_op->dirty_inode(inode, flags);
 
 		trace_writeback_dirty_inode(inode, flags);
-	}
-	if (flags & I_DIRTY_INODE)
+
 		flags &= ~I_DIRTY_TIME;
+	}
 	dirtytime = flags & I_DIRTY_TIME;
 
 	/*

index 2f56acc41c049..042b94288ff11 100644
@@ -562,8 +562,6 @@ static void gfs2_dirty_inode(struct inode *inode, int flags)
 	int need_endtrans = 0;
 	int ret;
 
-	if (!(flags & I_DIRTY_INODE))
-		return;
 	if (unlikely(gfs2_withdrawn(sdp)))
 		return;
 	if (!gfs2_glock_is_locked_by_me(ip->i_gl)) {

index b7616bbd55336..2e6064012f7d3 100644
@@ -2259,7 +2259,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 		trace_writeback_dirty_inode_start(inode, flags);
 
 		if (sb->s_op->dirty_inode)
-			sb->s_op->dirty_inode(inode, flags);
+			sb->s_op->dirty_inode(inode, flags & I_DIRTY_INODE);
 
 		trace_writeback_dirty_inode(inode, flags);
 

index 2e6064012f7d3..80ee9816d9df5 100644
@@ -2219,23 +2219,24 @@ static noinline void block_dump___mark_inode_dirty(struct inode *inode)
 }
 
 /**
- * __mark_inode_dirty -	internal function
+ * __mark_inode_dirty -	internal function to mark an inode dirty
  *
  * @inode: inode to mark
- * @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
+ * @flags: what kind of dirty, e.g. I_DIRTY_SYNC.  This can be a combination of
+ *	   multiple I_DIRTY_* flags, except that I_DIRTY_TIME can't be combined
+ *	   with I_DIRTY_PAGES.
  *
- * Mark an inode as dirty. Callers should use mark_inode_dirty or
- * mark_inode_dirty_sync.
+ * Mark an inode as dirty.  We notify the filesystem, then update the inode's
+ * dirty flags.  Then, if needed we add the inode to the appropriate dirty list.
  *
- * Put the inode on the super block's dirty list.
+ * Most callers should use mark_inode_dirty() or mark_inode_dirty_sync()
+ * instead of calling this directly.
  *
- * CAREFUL! We mark it dirty unconditionally, but move it onto the
- * dirty list only if it is hashed or if it refers to a blockdev.
- * If it was not hashed, it will never be added to the dirty list
- * even if it is later hashed, as it will have been marked dirty already.
+ * CAREFUL!  We only add the inode to the dirty list if it is hashed or if it
+ * refers to a blockdev.  Unhashed inodes will never be added to the dirty list
+ * even if they are later hashed, as they will have been marked dirty already.
  *
- * In short, make sure you hash any inodes _before_ you start marking
- * them dirty.
+ * In short, ensure you hash any inodes _before_ you start marking them dirty.
  *
  * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
  * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of

@@ -2247,25 +2248,34 @@ static noinline void block_dump___mark_inode_dirty(struct inode *inode)
 void __mark_inode_dirty(struct inode *inode, int flags)
 {
 	struct super_block *sb = inode->i_sb;
-	int dirtytime;
+	int dirtytime = 0;
 
 	trace_writeback_mark_inode_dirty(inode, flags);
 
-	/*
-	 * Don't do this for I_DIRTY_PAGES - that doesn't actually
-	 * dirty the inode itself
-	 */
 	if (flags & I_DIRTY_INODE) {
+		/*
+		 * Notify the filesystem about the inode being dirtied, so that
+		 * (if needed) it can update on-disk fields and journal the
+		 * inode.  This is only needed when the inode itself is being
+		 * dirtied now.  I.e. it's only needed for I_DIRTY_INODE, not
+		 * for just I_DIRTY_PAGES or I_DIRTY_TIME.
+		 */
 		trace_writeback_dirty_inode_start(inode, flags);
-
 		if (sb->s_op->dirty_inode)
 			sb->s_op->dirty_inode(inode, flags & I_DIRTY_INODE);
-
 		trace_writeback_dirty_inode(inode, flags);
 
+		/* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
 		flags &= ~I_DIRTY_TIME;
+	} else {
+		/*
+		 * Else it's either I_DIRTY_PAGES, I_DIRTY_TIME, or nothing.
+		 * (We don't support setting both I_DIRTY_PAGES and I_DIRTY_TIME
+		 * in one call to __mark_inode_dirty().)
+		 */
+		dirtytime = flags & I_DIRTY_TIME;
+		WARN_ON_ONCE(dirtytime && flags != I_DIRTY_TIME);
 	}
-	dirtytime = flags & I_DIRTY_TIME;
 
 	/*
 	 * Paired with smp_mb() in __writeback_single_inode() for the

@@ -2288,6 +2298,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 
 		inode_attach_wb(inode, NULL);
 
+		/* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
 		if (flags & I_DIRTY_INODE)
 			inode->i_state &= ~I_DIRTY_TIME;
 		inode->i_state |= flags;

index 80ee9816d9df5..cee1df6e3bd43 100644
@@ -1479,7 +1479,7 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 	 * change I_DIRTY_TIME into I_DIRTY_SYNC.
 	 */
 	if ((inode->i_state & I_DIRTY_TIME) &&
-	    (wbc->sync_mode == WB_SYNC_ALL || wbc->for_sync ||
+	    (wbc->sync_mode == WB_SYNC_ALL ||
 	     time_after(jiffies, inode->dirtied_time_when +
 			dirtytime_expire_interval * HZ))) {
 		trace_writeback_lazytime(inode);

index cee1df6e3bd43..e91980f493884 100644
@@ -1442,9 +1442,15 @@ static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
 }
 
 /*
- * Write out an inode and its dirty pages. Do not update the writeback list
- * linkage. That is left to the caller. The caller is also responsible for
- * setting I_SYNC flag and calling inode_sync_complete() to clear it.
+ * Write out an inode and its dirty pages (or some of its dirty pages, depending
+ * on @wbc->nr_to_write), and clear the relevant dirty flags from i_state.
+ *
+ * This doesn't remove the inode from the writeback list it is on, except
+ * potentially to move it from b_dirty_time to b_dirty due to timestamp
+ * expiration.  The caller is otherwise responsible for writeback list handling.
+ *
+ * The caller is also responsible for setting the I_SYNC flag beforehand and
+ * calling inode_sync_complete() to clear it afterwards.
  */
 static int
 __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)

@@ -1487,9 +1493,10 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 	}
 
 	/*
-	 * Some filesystems may redirty the inode during the writeback
-	 * due to delalloc, clear dirty metadata flags right before
-	 * write_inode()
+	 * Get and clear the dirty flags from i_state.  This needs to be done
+	 * after calling writepages because some filesystems may redirty the
+	 * inode during writepages due to delalloc.  It also needs to be done
+	 * after handling timestamp expiration, as that may dirty the inode too.
 	 */
 	spin_lock(&inode->i_lock);
 	dirty = inode->i_state & I_DIRTY;

@@ -1524,12 +1531,13 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 }
 
 /*
- * Write out an inode's dirty pages. Either the caller has an active reference
- * on the inode or the inode has I_WILL_FREE set.
+ * Write out an inode's dirty data and metadata on-demand, i.e. separately from
+ * the regular batched writeback done by the flusher threads in
+ * writeback_sb_inodes().  @wbc controls various aspects of the write, such as
+ * whether it is a data-integrity sync (%WB_SYNC_ALL) or not (%WB_SYNC_NONE).
  *
- * This function is designed to be called for writing back one inode which
- * we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
- * and does more profound writeback list handling in writeback_sb_inodes().
+ * To prevent the inode from going away, either the caller must have a reference
+ * to the inode, or the inode must have I_WILL_FREE or I_FREEING set.
  */
 static int writeback_single_inode(struct inode *inode,
 				  struct writeback_control *wbc)

@@ -1544,23 +1552,23 @@ static int writeback_single_inode(struct inode *inode,
 		WARN_ON(inode->i_state & I_WILL_FREE);
 
 	if (inode->i_state & I_SYNC) {
-		if (wbc->sync_mode != WB_SYNC_ALL)
-			goto out;
 		/*
-		 * It's a data-integrity sync. We must wait. Since callers hold
-		 * inode reference or inode has I_WILL_FREE set, it cannot go
-		 * away under us.
+		 * Writeback is already running on the inode.  For WB_SYNC_NONE,
+		 * that's enough and we can just return.  For WB_SYNC_ALL, we
+		 * must wait for the existing writeback to complete, then do
+		 * writeback again if there's anything left.
 		 */
+		if (wbc->sync_mode != WB_SYNC_ALL)
+			goto out;
 		__inode_wait_for_writeback(inode);
 	}
 	WARN_ON(inode->i_state & I_SYNC);
 	/*
-	 * Skip inode if it is clean and we have no outstanding writeback in
-	 * WB_SYNC_ALL mode. We don't want to mess with writeback lists in this
-	 * function since flusher thread may be doing for example sync in
-	 * parallel and if we move the inode, it could get skipped. So here we
-	 * make sure inode is on some writeback list and leave it there unless
-	 * we have completely cleaned the inode.
+	 * If the inode is already fully clean, then there's nothing to do.
+	 *
+	 * For data-integrity syncs we also need to check whether any pages are
+	 * still under writeback, e.g. due to prior WB_SYNC_NONE writeback.  If
+	 * there are any such pages, we'll need to wait for them.
 	 */
 	if (!(inode->i_state & I_DIRTY_ALL) &&
 	    (wbc->sync_mode != WB_SYNC_ALL ||

@@ -1576,8 +1584,9 @@ static int writeback_single_inode(struct inode *inode,
 	wb = inode_to_wb_and_lock_list(inode);
 	spin_lock(&inode->i_lock);
 	/*
-	 * If inode is clean, remove it from writeback lists. Otherwise don't
-	 * touch it. See comment above for explanation.
+	 * If the inode is now fully clean, then it can be safely removed from
+	 * its writeback list (if any).  Otherwise the flusher threads are
+	 * responsible for the writeback lists.
 	 */
 	if (!(inode->i_state & I_DIRTY_ALL))
 		inode_io_list_del_locked(inode, wb);

index b39b339feddc9..7fe2497755a37 100644
@@ -749,7 +749,7 @@ static int gfs2_fsync(struct file *file, loff_t start, loff_t end,
 {
 	struct address_space *mapping = file->f_mapping;
 	struct inode *inode = mapping->host;
-	int sync_state = inode->i_state & I_DIRTY_ALL;
+	int sync_state = inode->i_state & I_DIRTY;
 	struct gfs2_inode *ip = GFS2_I(inode);
 	int ret = 0, ret1 = 0;
 

@@ -762,7 +762,7 @@ static int gfs2_fsync(struct file *file, loff_t start, loff_t end,
 	if (!gfs2_is_jdata(ip))
 		sync_state &= ~I_DIRTY_PAGES;
 	if (datasync)
-		sync_state &= ~(I_DIRTY_SYNC | I_DIRTY_TIME);
+		sync_state &= ~I_DIRTY_SYNC;
 
 	if (sync_state) {
 		ret = sync_inode_metadata(inode, 1);

index 4cc6c7834312f..d809a06b6ef7f 100644
@@ -4961,15 +4961,11 @@ static void __ext4_update_other_inode_time(struct super_block *sb,
 	if (!inode)
 		return;
 
-	if ((inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW |
-			       I_DIRTY_INODE)) ||
-	    ((inode->i_state & I_DIRTY_TIME) == 0))
+	if (!inode_is_dirtytime_only(inode))
 		return;
 
 	spin_lock(&inode->i_lock);
-	if (((inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW |
-				I_DIRTY_INODE)) == 0) &&
-	    (inode->i_state & I_DIRTY_TIME)) {
+	if (inode_is_dirtytime_only(inode)) {
 		struct ext4_inode_info	*ei = EXT4_I(inode);
 
 		inode->i_state &= ~I_DIRTY_TIME;

index 45a0303b2aeb6..de0c789104c26 100644
@@ -2194,6 +2194,21 @@ static inline void mark_inode_dirty_sync(struct inode *inode)
 	__mark_inode_dirty(inode, I_DIRTY_SYNC);
 }
 
+/*
+ * Returns true if the given inode itself only has dirty timestamps (its pages
+ * may still be dirty) and isn't currently being allocated or freed.
+ * Filesystems should call this if when writing an inode when lazytime is
+ * enabled, they want to opportunistically write the timestamps of other inodes
+ * located very nearby on-disk, e.g. in the same inode block.  This returns true
+ * if the given inode is in need of such an opportunistic update.  Requires
+ * i_lock, or at least later re-checking under i_lock.
+ */
+static inline bool inode_is_dirtytime_only(struct inode *inode)
+{
+	return (inode->i_state & (I_DIRTY_TIME | I_NEW |
+				  I_FREEING | I_WILL_FREE)) == I_DIRTY_TIME;
+}
+
 extern void inc_nlink(struct inode *inode);
 extern void drop_nlink(struct inode *inode);
 extern void clear_nlink(struct inode *inode);