[PATCH v3 16/19] netfs: Fix netfs_read_folio() to wait on writeback

[David Howells <dhowells@redhat.com>]

Fix netfs_read_folio() to wait for an ongoing writeback to complete so that
it can trust the dirty flag and whatever is attached to folio->private
(folio->private may get cleaned up by the collector before it clears the
writeback flag).

Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading")
Closes: https://sashiko.dev/#/patchset/20260414082004.3756080-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Paulo Alcantara <pc@manguebit.org>
cc: Matthew Wilcox <willy@infradead.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/buffered_read.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
index f1cbd6e10ad7..2de849bd780f 100644
--- a/fs/netfs/buffered_read.c
+++ b/fs/netfs/buffered_read.c
@@ -506,6 +506,8 @@ int netfs_read_folio(struct file *file, struct folio *folio)
 	struct netfs_inode *ctx = netfs_inode(mapping->host);
 	int ret;
 
+	folio_wait_writeback(folio);
+
 	if (folio_test_dirty(folio))
 		return netfs_read_gaps(file, folio);