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>

10 files changed, 23 insertions, 30 deletions

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 82690d1dd49a..f92b9e62d567 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -319,16 +319,16 @@ expand:
 		struct folio *folio;
 
 		folio = filemap_get_folio(mapping, i);
-		if (!folio) {
+		if (IS_ERR(folio)) {
 			if (test_and_clear_bit(AFS_VNODE_DIR_VALID, &dvnode->flags))
 				afs_stat_v(dvnode, n_inval);
-
-			ret = -ENOMEM;
 			folio = __filemap_get_folio(mapping,
 						    i, FGP_LOCK | FGP_CREAT,
 						    mapping->gfp_mask);
-			if (!folio)
+			if (IS_ERR(folio)) {
+				ret = PTR_ERR(folio);
 				goto error;
+			}
 			folio_attach_private(folio, (void *)1);
 			folio_unlock(folio);
 		}
@@ -524,7 +524,7 @@ static int afs_dir_iterate(struct inode *dir, struct dir_context *ctx,
 		 */
 		folio = __filemap_get_folio(dir->i_mapping, ctx->pos / PAGE_SIZE,
 					    FGP_ACCESSED, 0);
-		if (!folio) {
+		if (IS_ERR(folio)) {
 			ret = afs_bad(dvnode, afs_file_error_dir_missing_page);
 			break;
 		}
diff --git a/fs/afs/dir_edit.c b/fs/afs/dir_edit.c
index 0ab7752d1b75..f0eddccbdd95 100644
--- a/fs/afs/dir_edit.c
+++ b/fs/afs/dir_edit.c
@@ -115,7 +115,7 @@ static struct folio *afs_dir_get_folio(struct afs_vnode *vnode, pgoff_t index)
 	folio = __filemap_get_folio(mapping, index,
 				    FGP_LOCK | FGP_ACCESSED | FGP_CREAT,
 				    mapping->gfp_mask);
-	if (!folio)
+	if (IS_ERR(folio))
 		clear_bit(AFS_VNODE_DIR_VALID, &vnode->flags);
 	else if (folio && !folio_test_private(folio))
 		folio_attach_private(folio, (void *)1);
diff --git a/fs/afs/write.c b/fs/afs/write.c
index 571f3b9a417e..c822d6006033 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -232,7 +232,7 @@ static void afs_kill_pages(struct address_space *mapping,
 		_debug("kill %lx (to %lx)", index, last);
 
 		folio = filemap_get_folio(mapping, index);
-		if (!folio) {
+		if (IS_ERR(folio)) {
 			next = index + 1;
 			continue;
 		}
@@ -270,7 +270,7 @@ static void afs_redirty_pages(struct writeback_control *wbc,
 		_debug("redirty %llx @%llx", len, start);
 
 		folio = filemap_get_folio(mapping, index);
-		if (!folio) {
+		if (IS_ERR(folio)) {
 			next = index + 1;
 			continue;
 		}
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index bf0b7dea4900..d7973743417b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5395,7 +5395,7 @@ static void ext4_wait_for_tail_page_commit(struct inode *inode)
 	while (1) {
 		struct folio *folio = filemap_lock_folio(inode->i_mapping,
 				      inode->i_size >> PAGE_SHIFT);
-		if (!folio)
+		if (IS_ERR(folio))
 			return;
 		ret = __ext4_journalled_invalidate_folio(folio, offset,
 						folio_size(folio) - offset);
diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index 2de9829aed63..7bf6d069199c 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -141,18 +141,18 @@ mext_folio_double_lock(struct inode *inode1, struct inode *inode2,
 	flags = memalloc_nofs_save();
 	folio[0] = __filemap_get_folio(mapping[0], index1, fgp_flags,
 			mapping_gfp_mask(mapping[0]));
-	if (!folio[0]) {
+	if (IS_ERR(folio[0])) {
 		memalloc_nofs_restore(flags);
-		return -ENOMEM;
+		return PTR_ERR(folio[0]);
 	}
 
 	folio[1] = __filemap_get_folio(mapping[1], index2, fgp_flags,
 			mapping_gfp_mask(mapping[1]));
 	memalloc_nofs_restore(flags);
-	if (!folio[1]) {
+	if (IS_ERR(folio[1])) {
 		folio_unlock(folio[0]);
 		folio_put(folio[0]);
-		return -ENOMEM;
+		return PTR_ERR(folio[1]);
 	}
 	/*
 	 * __filemap_get_folio() may not wait on folio's writeback if
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 9062da6da567..702d79639c0d 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -697,7 +697,7 @@ static void hugetlbfs_zero_partial_page(struct hstate *h,
 	struct folio *folio;
 
 	folio = filemap_lock_folio(mapping, idx);
-	if (!folio)
+	if (IS_ERR(folio))
 		return;
 
 	start = start & ~huge_page_mask(h);
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 6f4c97a6d7e9..96bb56c203f4 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -468,19 +468,12 @@ EXPORT_SYMBOL_GPL(iomap_is_partially_uptodate);
 struct folio *iomap_get_folio(struct iomap_iter *iter, loff_t pos)
 {
 	unsigned fgp = FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE | FGP_NOFS;
-	struct folio *folio;
 
 	if (iter->flags & IOMAP_NOWAIT)
 		fgp |= FGP_NOWAIT;
 
-	folio = __filemap_get_folio(iter->inode->i_mapping, pos >> PAGE_SHIFT,
+	return __filemap_get_folio(iter->inode->i_mapping, pos >> PAGE_SHIFT,
 			fgp, mapping_gfp_mask(iter->inode->i_mapping));
-	if (folio)
-		return folio;
-
-	if (iter->flags & IOMAP_NOWAIT)
-		return ERR_PTR(-EAGAIN);
-	return ERR_PTR(-ENOMEM);
 }
 EXPORT_SYMBOL_GPL(iomap_get_folio);
 
@@ -911,7 +904,7 @@ static int iomap_write_delalloc_scan(struct inode *inode,
 		/* grab locked page */
 		folio = filemap_lock_folio(inode->i_mapping,
 				start_byte >> PAGE_SHIFT);
-		if (!folio) {
+		if (IS_ERR(folio)) {
 			start_byte = ALIGN_DOWN(start_byte, PAGE_SIZE) +
 					PAGE_SIZE;
 			continue;
diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
index 7679a68e8193..209726a9cfdb 100644
--- a/fs/netfs/buffered_read.c
+++ b/fs/netfs/buffered_read.c
@@ -350,8 +350,8 @@ int netfs_write_begin(struct netfs_inode *ctx,
 retry:
 	folio = __filemap_get_folio(mapping, index, fgp_flags,
 				    mapping_gfp_mask(mapping));
-	if (!folio)
-		return -ENOMEM;
+	if (IS_ERR(folio))
+		return PTR_ERR(folio);
 
 	if (ctx->ops->check_write_begin) {
 		/* Allow the netfs (eg. ceph) to flush conflicts. */
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 893625eacab9..1d03406e6c03 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -336,8 +336,8 @@ static int nfs_write_begin(struct file *file, struct address_space *mapping,
 
 start:
 	folio = nfs_folio_grab_cache_write_begin(mapping, pos >> PAGE_SHIFT);
-	if (!folio)
-		return -ENOMEM;
+	if (IS_ERR(folio))
+		return PTR_ERR(folio);
 	*pagep = &folio->page;
 
 	ret = nfs_flush_incompatible(file, folio);
diff --git a/fs/nilfs2/page.c b/fs/nilfs2/page.c
index 41ccd43cd979..5cf30827f244 100644
--- a/fs/nilfs2/page.c
+++ b/fs/nilfs2/page.c
@@ -259,10 +259,10 @@ repeat:
 			NILFS_PAGE_BUG(&folio->page, "inconsistent dirty state");
 
 		dfolio = filemap_grab_folio(dmap, folio->index);
-		if (unlikely(!dfolio)) {
+		if (unlikely(IS_ERR(dfolio))) {
 			/* No empty page is added to the page cache */
-			err = -ENOMEM;
 			folio_unlock(folio);
+			err = PTR_ERR(dfolio);
 			break;
 		}
 		if (unlikely(!folio_buffers(folio)))
@@ -311,7 +311,7 @@ repeat:
 
 		folio_lock(folio);
 		dfolio = filemap_lock_folio(dmap, index);
-		if (dfolio) {
+		if (!IS_ERR(dfolio)) {
 			/* overwrite existing folio in the destination cache */
 			WARN_ON(folio_test_dirty(dfolio));
 			nilfs_copy_page(&dfolio->page, &folio->page, 0);