[PATCH v1 2/2] fs/writeback: skip inodes with potential writeback hang in wait_sb_inodes()

[Joanne Koong <joannelkoong@gmail.com>]

During superblock writeback waiting, skip inodes where writeback may
take an indefinite amount of time or hang, as denoted by the
AS_WRITEBACK_MAY_HANG mapping flag.

Currently, fuse is the only filesystem with this flag set. For a
properly functioning fuse server, writeback requests are completed and
there is no issue. However, if there is a bug in the fuse server and it
hangs on writeback, then without this change, wait_sb_inodes() will wait
forever.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Fixes: 0c58a97f919c ("fuse: remove tmp folio for writebacks and internal rb tree")
Reported-by: Athul Krishna <athul.krishna.kr@protonmail.com>
---
 fs/fs-writeback.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 2b35e80037fe..eb246e9fbf3d 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -2733,6 +2733,9 @@ static void wait_sb_inodes(struct super_block *sb)
 		if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
 			continue;
 
+		if (mapping_writeback_may_hang(mapping))
+			continue;
+
 		spin_unlock_irq(&sb->s_inode_wblist_lock);
 
 		spin_lock(&inode->i_lock);
-- 
2.47.3