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.

[hch@lst.de: fix null-pointer deref]
  Link: https://lkml.kernel.org/r/20230310070023.GA13563@lst.de
  Link: https://lkml.kernel.org/r/20230310043137.GA1624890@u2004
Link: https://lkml.kernel.org/r/20230307143410.28031-8-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Ryusuke Konishi <konishi.ryusuke@gmail.com> [nilfs2]
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 10 insertions, 7 deletions

diff --git a/mm/swap_state.c b/mm/swap_state.c
index 92234f4b51d2..b76a65ac28b3 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -336,7 +336,7 @@ struct folio *swap_cache_get_folio(swp_entry_t entry,
 	struct folio *folio;
 
 	folio = filemap_get_folio(swap_address_space(entry), swp_offset(entry));
-	if (folio) {
+	if (!IS_ERR(folio)) {
 		bool vma_ra = swap_use_vma_readahead();
 		bool readahead;
 
@@ -366,6 +366,8 @@ struct folio *swap_cache_get_folio(swp_entry_t entry,
 			if (!vma || !vma_ra)
 				atomic_inc(&swapin_readahead_hits);
 		}
+	} else {
+		folio = NULL;
 	}
 
 	return folio;
@@ -388,23 +390,24 @@ struct folio *filemap_get_incore_folio(struct address_space *mapping,
 	struct swap_info_struct *si;
 	struct folio *folio = filemap_get_entry(mapping, index);
 
+	if (!folio)
+		return ERR_PTR(-ENOENT);
 	if (!xa_is_value(folio))
-		goto out;
+		return folio;
 	if (!shmem_mapping(mapping))
-		return NULL;
+		return ERR_PTR(-ENOENT);
 
 	swp = radix_to_swp_entry(folio);
 	/* There might be swapin error entries in shmem mapping. */
 	if (non_swap_entry(swp))
-		return NULL;
+		return ERR_PTR(-ENOENT);
 	/* Prevent swapoff from happening to us */
 	si = get_swap_device(swp);
 	if (!si)
-		return NULL;
+		return ERR_PTR(-ENOENT);
 	index = swp_offset(swp);
 	folio = filemap_get_folio(swap_address_space(swp), index);
 	put_swap_device(si);
-out:
 	return folio;
 }
 
@@ -431,7 +434,7 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 		folio = filemap_get_folio(swap_address_space(entry),
 						swp_offset(entry));
 		put_swap_device(si);
-		if (folio)
+		if (!IS_ERR(folio))
 			return folio_file_page(folio, swp_offset(entry));
 
 		/*