[PATCH v6 20/24] netfs: Fix partial invalidation of streaming-write folio

In netfs_invalidate_folio(), if the region of a partial invalidation
overlaps the front (but not all) of a dirty write cached in a streaming
write page (dirty, but not uptodate, with the dirty region tracked by a
netfs_folio struct), the function modifies the dirty region - but
incorrectly as it moves the region forward by setting the start to the
start, not the end, of the invalidation region.

Fix this by setting finfo->dirty_offset to the end of the invalidation
region (iend).

Fixes: cce6bfa6ca0e ("netfs: Fix trimming of streaming-write folios in netfs_inval_folio()")
Closes: https://sashiko.dev/#/patchset/20260414082004.3756080-1-dhowells%40redhat.com
Signed-off-by: David Howells <[email protected]>
cc: Paulo Alcantara <[email protected]>
cc: Matthew Wilcox <[email protected]>
cc: [email protected]
cc: [email protected]
---
 fs/netfs/misc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/netfs/misc.c b/fs/netfs/misc.c
index 24b20e80e9a8..5d554512ed23 100644
--- a/fs/netfs/misc.c
+++ b/fs/netfs/misc.c
@@ -262,7 +262,7 @@ void netfs_invalidate_folio(struct folio *folio, size_t offset, size_t length)
 				goto erase_completely;
 			/* Move the start of the data. */
 			finfo->dirty_len = fend - iend;
-			finfo->dirty_offset = offset;
+			finfo->dirty_offset = iend;
 			trace_netfs_folio(folio, netfs_folio_trace_invalidate_front);
 			return;
 		}