[PATCH v5 3/5] fs/writeback: in wait_sb_inodes(), skip wait for AS_WRITEBACK_INDETERMINATE mappings

[Joanne Koong <joannelkoong@gmail.com>]

For filesystems with the AS_WRITEBACK_INDETERMINATE flag set, writeback
operations may take an indeterminate time to complete. For example, writing
data back to disk in FUSE filesystems depends on the userspace server
successfully completing writeback.

In this commit, wait_sb_inodes() skips waiting on writeback if the
inode's mapping has AS_WRITEBACK_INDETERMINATE set, else sync(2) may take an
indeterminate amount of time to complete.

If the caller wishes to ensure the data for a mapping with the
AS_WRITEBACK_INDETERMINATE flag set has actually been written back to disk,
they should use fsync(2)/fdatasync(2) instead.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 fs/fs-writeback.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index d8bec3c1bb1f..ad192db17ce4 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -2659,6 +2659,9 @@ static void wait_sb_inodes(struct super_block *sb)
 		if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
 			continue;
 
+		if (mapping_writeback_indeterminate(mapping))
+			continue;
+
 		spin_unlock_irq(&sb->s_inode_wblist_lock);
 
 		spin_lock(&inode->i_lock);
-- 
2.43.5