mm: return an ERR_PTR from __filemap_get_folio

Instead of returning NULL for all errors, distinguish between:

 - no entry found and not asked to allocated (-ENOENT)
 - failed to allocate memory (-ENOMEM)
 - would block (-EAGAIN)

so that callers don't have to guess the error based on the passed in
flags.

Also pass through the error through the direct callers: filemap_get_folio,
filemap_lock_folio filemap_grab_folio and filemap_get_incore_folio.

[[email protected]: fix null-pointer deref]
  Link: https://lkml.kernel.org/r/[email protected]
  Link: https://lkml.kernel.org/r/20230310043137.GA1624890@u2004
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Christoph Hellwig <[email protected]>
Acked-by: Ryusuke Konishi <[email protected]> [nilfs2]
Cc: Andreas Gruenbacher <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 8 insertions, 7 deletions

diff --git a/mm/truncate.c b/mm/truncate.c
index 7b4ea4c4a46b..86de31ed4d32 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -375,7 +375,7 @@ void truncate_inode_pages_range(struct address_space *mapping,
 
 	same_folio = (lstart >> PAGE_SHIFT) == (lend >> PAGE_SHIFT);
 	folio = __filemap_get_folio(mapping, lstart >> PAGE_SHIFT, FGP_LOCK, 0);
-	if (folio) {
+	if (!IS_ERR(folio)) {
 		same_folio = lend < folio_pos(folio) + folio_size(folio);
 		if (!truncate_inode_partial_folio(folio, lstart, lend)) {
 			start = folio->index + folio_nr_pages(folio);
@@ -387,14 +387,15 @@ void truncate_inode_pages_range(struct address_space *mapping,
 		folio = NULL;
 	}
 
-	if (!same_folio)
+	if (!same_folio) {
 		folio = __filemap_get_folio(mapping, lend >> PAGE_SHIFT,
 						FGP_LOCK, 0);
-	if (folio) {
-		if (!truncate_inode_partial_folio(folio, lstart, lend))
-			end = folio->index;
-		folio_unlock(folio);
-		folio_put(folio);
+		if (!IS_ERR(folio)) {
+			if (!truncate_inode_partial_folio(folio, lstart, lend))
+				end = folio->index;
+			folio_unlock(folio);
+			folio_put(folio);
+		}
 	}
 
 	index = start;