netfs: Fix netfs_release_folio() to say no if folio dirty

Fix netfs_release_folio() to say no (ie. return false) if the folio is
dirty (analogous with iomap's behaviour).  Without this, it will say yes to
the release of a dirty page by split_huge_page_to_list_to_order(), which
will result in the loss of untruncated data in the folio.

Without this, the generic/075 and generic/112 xfstests (both fsx-based
tests) fail with minimum folio size patches applied[1].

Fixes: c1ec4d7 ("netfs: Provide invalidate_folio and release_folio calls")
Signed-off-by: David Howells <[email protected]>
Link: https://lore.kernel.org/r/[email protected]/ [1]
Link: https://lore.kernel.org/r/[email protected]
cc: Matthew Wilcox (Oracle) <[email protected]>
cc: Pankaj Raghav <[email protected]>
cc: Jeff Layton <[email protected]>
cc: Marc Dionne <[email protected]>
cc: [email protected]
cc: [email protected]
cc: [email protected]
cc: [email protected]
Signed-off-by: Christian Brauner <[email protected]>

Author: dhowells

fs/netfs/misc.c

@@ -161,6 +161,9 @@ bool netfs_release_folio(struct folio *folio, gfp_t gfp)
 	struct netfs_inode *ctx = netfs_inode(folio_inode(folio));
 	unsigned long long end;
 
+	if (folio_test_dirty(folio))
+		return false;
+
 	end = folio_pos(folio) + folio_size(folio);
 	if (end > ctx->zero_point)
 		ctx->zero_point = end;