[PATCH] gfs2: fix hung task in gfs2_jhead_process_page

[Deepanshu Kartikey]

filemap_get_folio() returns an ERR_PTR if the folio is not present
in the page cache. gfs2_jhead_process_page() does not check the
return value and passes it directly to folio_wait_locked(), causing
the kernel task to get stuck in uninterruptible sleep (state D)
forever, triggering the hung task watchdog.

This can be triggered by mounting a crafted or corrupted GFS2
filesystem image.

Fix this by checking the return value of filemap_get_folio() and
returning early if the folio is not found.

Fixes: 240159077d00 ("gfs2: Convert gfs2_jhead_process_page() to use a folio")
Reported-by: syzbot+9013411dc43f3582823a@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=9013411dc43f3582823a
Signed-off-by: Deepanshu Kartikey <Kartikey406@xxxxxxxxx>
---
 fs/gfs2/lops.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index 797931eb5845..005584311eff 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -467,6 +467,9 @@ static void gfs2_jhead_process_page(struct gfs2_jdesc *jd, unsigned long index,
 
 	folio = filemap_get_folio(jd->jd_inode->i_mapping, index);
 
+	if (IS_ERR(folio))
+		return;
+
 	folio_wait_locked(folio);
 	if (!folio_test_uptodate(folio))
 		*done = true;
-- 
2.43.0