return an ERR_PTR from __filemap_get_folio v2

return an ERR_PTR from __filemap_get_folio v2

[Christoph Hellwig]

Hi all,

__filemap_get_folio and its wrappers can return NULL for three different
conditions, which in some cases requires the caller to reverse engineer
the decision making.  This is fixed by returning an ERR_PTR instead of
NULL and thus transporting the reason for the failure.  But to make
that work we first need to ensure that no xa_value special case is
returned and thus return the FGP_ENTRY flag.  It turns out that flag
is barely used and can usually be deal with in a better way.

Note that the shmem patches in here are non-trivial and need some
careful review and testing.

Changes since v1:
 - drop the patches to check for errors in btrfs and gfs2
 - document the new calling conventions for the wrappers around
   __filemap_get_folio
 - rebased against the iomap changes in latest linux-next

Diffstat
 fs/afs/dir.c             |   10 +++----
 fs/afs/dir_edit.c        |    2 -
 fs/afs/write.c           |    4 +-
 fs/btrfs/disk-io.c       |    2 -
 fs/ext4/inode.c          |    2 -
 fs/ext4/move_extent.c    |    8 ++---
 fs/hugetlbfs/inode.c     |    2 -
 fs/iomap/buffered-io.c   |   15 +----------
 fs/netfs/buffered_read.c |    4 +-
 fs/nilfs2/page.c         |    6 ++--
 include/linux/pagemap.h  |   15 +++++------
 include/linux/shmem_fs.h |    1 
 mm/filemap.c             |   27 ++++++++-----------
 mm/folio-compat.c        |    4 +-
 mm/huge_memory.c         |    5 +--
 mm/memcontrol.c          |    2 -
 mm/mincore.c             |    2 -
 mm/shmem.c               |   64 +++++++++++++++++++----------------------------
 mm/swap_state.c          |   17 ++++++------
 mm/swapfile.c            |    4 +-
 mm/truncate.c            |   15 +++++------
 21 files changed, 94 insertions(+), 117 deletions(-)

[PATCH 1/7] mm: don't look at xarray value entries in split_huge_pages_in_file

[Christoph Hellwig]

split_huge_pages_in_file never wants to do anything with the special
value enties.  Switch to using filemap_get_folio to not even see them.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/huge_memory.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 1d6977dc6b31ba..a2830019aaa017 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3100,11 +3100,10 @@ static int split_huge_pages_in_file(const char *file_path, pgoff_t off_start,
 	mapping = candidate->f_mapping;
 
 	for (index = off_start; index < off_end; index += nr_pages) {
-		struct folio *folio = __filemap_get_folio(mapping, index,
-						FGP_ENTRY, 0);
+		struct folio *folio = filemap_get_folio(mapping, index);
 
 		nr_pages = 1;
-		if (xa_is_value(folio) || !folio)
+		if (!folio)
 			continue;
 
 		if (!folio_test_large(folio))
-- 
2.39.0

[PATCH 2/7] mm: make mapping_get_entry available outside of filemap.c

[Christoph Hellwig]

mapping_get_entry is useful for page cache API users that need to know
about xa_value internals.  Rename it and make it available in pagemap.h.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/pagemap.h | 1 +
 mm/filemap.c            | 6 +++---
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 9f108168377195..24dedf6b12be49 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -507,6 +507,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
 #define FGP_ENTRY		0x00000080
 #define FGP_STABLE		0x00000100
 
+void *filemap_get_entry(struct address_space *mapping, pgoff_t index);
 struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 		int fgp_flags, gfp_t gfp);
 struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
diff --git a/mm/filemap.c b/mm/filemap.c
index c915ded191f03f..ed0583f9e27512 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1834,7 +1834,7 @@ EXPORT_SYMBOL(page_cache_prev_miss);
  */
 
 /*
- * mapping_get_entry - Get a page cache entry.
+ * filemap_get_entry - Get a page cache entry.
  * @mapping: the address_space to search
  * @index: The page cache index.
  *
@@ -1845,7 +1845,7 @@ EXPORT_SYMBOL(page_cache_prev_miss);
  *
  * Return: The folio, swap or shadow entry, %NULL if nothing is found.
  */
-static void *mapping_get_entry(struct address_space *mapping, pgoff_t index)
+void *filemap_get_entry(struct address_space *mapping, pgoff_t index)
 {
 	XA_STATE(xas, &mapping->i_pages, index);
 	struct folio *folio;
@@ -1915,7 +1915,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 	struct folio *folio;
 
 repeat:
-	folio = mapping_get_entry(mapping, index);
+	folio = filemap_get_entry(mapping, index);
 	if (xa_is_value(folio)) {
 		if (fgp_flags & FGP_ENTRY)
 			return folio;
-- 
2.39.0

[PATCH 3/7] mm: use filemap_get_entry in filemap_get_incore_folio

[Christoph Hellwig]

filemap_get_incore_folio wants to look at the details of xa_is_value
entries, but doesn't need any of the other logic in filemap_get_folio.
Switch it to use the lower-level filemap_get_entry interface.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/swap_state.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index 7a003d8abb37bc..92234f4b51d29a 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -386,7 +386,7 @@ struct folio *filemap_get_incore_folio(struct address_space *mapping,
 {
 	swp_entry_t swp;
 	struct swap_info_struct *si;
-	struct folio *folio = __filemap_get_folio(mapping, index, FGP_ENTRY, 0);
+	struct folio *folio = filemap_get_entry(mapping, index);
 
 	if (!xa_is_value(folio))
 		goto out;
-- 
2.39.0

[PATCH 4/7] shmem: remove shmem_get_partial_folio

[Christoph Hellwig]

Add a new SGP_FIND mode for shmem_get_partial_folio that works like
SGP_READ, but does not check i_size.  Use that instead of open coding
the page cache lookup in shmem_get_partial_folio.  Note that this is
a behavior change in that it reads in swap cache entries for offsets
outside i_size, possibly causing a little bit of extra work.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/shmem_fs.h |  1 +
 mm/shmem.c               | 46 ++++++++++++----------------------------
 2 files changed, 15 insertions(+), 32 deletions(-)

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index d09d54be4ffd99..7ba160ac066e5e 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -105,6 +105,7 @@ enum sgp_type {
 	SGP_CACHE,	/* don't exceed i_size, may allocate page */
 	SGP_WRITE,	/* may exceed i_size, may allocate !Uptodate page */
 	SGP_FALLOC,	/* like SGP_WRITE, but make existing page Uptodate */
+	SGP_FIND,	/* like SGP_READ, but also read outside i_size */
 };
 
 int shmem_get_folio(struct inode *inode, pgoff_t index, struct folio **foliop,
diff --git a/mm/shmem.c b/mm/shmem.c
index de6fa3980c7d6b..a8371ffeeee54a 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -877,27 +877,6 @@ void shmem_unlock_mapping(struct address_space *mapping)
 	}
 }
 
-static struct folio *shmem_get_partial_folio(struct inode *inode, pgoff_t index)
-{
-	struct folio *folio;
-
-	/*
-	 * At first avoid shmem_get_folio(,,,SGP_READ): that fails
-	 * beyond i_size, and reports fallocated pages as holes.
-	 */
-	folio = __filemap_get_folio(inode->i_mapping, index,
-					FGP_ENTRY | FGP_LOCK, 0);
-	if (!xa_is_value(folio))
-		return folio;
-	/*
-	 * But read a page back from swap if any of it is within i_size
-	 * (although in some cases this is just a waste of time).
-	 */
-	folio = NULL;
-	shmem_get_folio(inode, index, &folio, SGP_READ);
-	return folio;
-}
-
 /*
  * Remove range of pages and swap entries from page cache, and free them.
  * If !unfalloc, truncate or punch hole; if unfalloc, undo failed fallocate.
@@ -957,7 +936,8 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
 		goto whole_folios;
 
 	same_folio = (lstart >> PAGE_SHIFT) == (lend >> PAGE_SHIFT);
-	folio = shmem_get_partial_folio(inode, lstart >> PAGE_SHIFT);
+	folio = NULL;
+	shmem_get_folio(inode, lstart >> PAGE_SHIFT, &folio, SGP_FIND);
 	if (folio) {
 		same_folio = lend < folio_pos(folio) + folio_size(folio);
 		folio_mark_dirty(folio);
@@ -971,14 +951,16 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
 		folio = NULL;
 	}
 
-	if (!same_folio)
-		folio = shmem_get_partial_folio(inode, lend >> PAGE_SHIFT);
-	if (folio) {
-		folio_mark_dirty(folio);
-		if (!truncate_inode_partial_folio(folio, lstart, lend))
-			end = folio->index;
-		folio_unlock(folio);
-		folio_put(folio);
+	if (!same_folio) {
+		folio = NULL;
+		shmem_get_folio(inode, lend >> PAGE_SHIFT, &folio, SGP_FIND);
+		if (folio) {
+			folio_mark_dirty(folio);
+			if (!truncate_inode_partial_folio(folio, lstart, lend))
+				end = folio->index;
+			folio_unlock(folio);
+			folio_put(folio);
+		}
 	}
 
 whole_folios:
@@ -1900,7 +1882,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
 		if (folio_test_uptodate(folio))
 			goto out;
 		/* fallocated folio */
-		if (sgp != SGP_READ)
+		if (sgp != SGP_READ && sgp != SGP_FIND)
 			goto clear;
 		folio_unlock(folio);
 		folio_put(folio);
@@ -1911,7 +1893,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
 	 * SGP_NOALLOC: fail on hole, with NULL folio, letting caller fail.
 	 */
 	*foliop = NULL;
-	if (sgp == SGP_READ)
+	if (sgp == SGP_READ || sgp == SGP_FIND)
 		return 0;
 	if (sgp == SGP_NOALLOC)
 		return -ENOENT;
-- 
2.39.0

[PATCH 5/7] shmem: open code the page cache lookup in shmem_get_folio_gfp

[Christoph Hellwig]

Use the very low level filemap_get_entry helper to look up the
entry in the xarray, and then:

 - don't bother locking the folio if only doing a userfault notification
 - open code locking the page and checking for truncation in a related
   code block

This will allow to eventually remove the FGP_ENTRY flag.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 mm/shmem.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index a8371ffeeee54a..23d5cf8182cb1f 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1856,12 +1856,10 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
 	sbinfo = SHMEM_SB(inode->i_sb);
 	charge_mm = vma ? vma->vm_mm : NULL;
 
-	folio = __filemap_get_folio(mapping, index, FGP_ENTRY | FGP_LOCK, 0);
+	folio = filemap_get_entry(mapping, index);
 	if (folio && vma && userfaultfd_minor(vma)) {
-		if (!xa_is_value(folio)) {
-			folio_unlock(folio);
+		if (!xa_is_value(folio))
 			folio_put(folio);
-		}
 		*fault_type = handle_userfault(vmf, VM_UFFD_MINOR);
 		return 0;
 	}
@@ -1877,6 +1875,14 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
 	}
 
 	if (folio) {
+		folio_lock(folio);
+
+		/* Has the page been truncated? */
+		if (unlikely(folio->mapping != mapping)) {
+			folio_unlock(folio);
+			folio_put(folio);
+			goto repeat;
+		}
 		if (sgp == SGP_WRITE)
 			folio_mark_accessed(folio);
 		if (folio_test_uptodate(folio))
-- 
2.39.0

[PATCH 6/7] mm: remove FGP_ENTRY

[Christoph Hellwig]

FGP_ENTRY is unused now, so remove it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/pagemap.h | 3 +--
 mm/filemap.c            | 7 +------
 mm/folio-compat.c       | 4 ++--
 3 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 24dedf6b12be49..e2208ee36966ea 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -504,8 +504,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
 #define FGP_NOFS		0x00000010
 #define FGP_NOWAIT		0x00000020
 #define FGP_FOR_MMAP		0x00000040
-#define FGP_ENTRY		0x00000080
-#define FGP_STABLE		0x00000100
+#define FGP_STABLE		0x00000080
 
 void *filemap_get_entry(struct address_space *mapping, pgoff_t index);
 struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
diff --git a/mm/filemap.c b/mm/filemap.c
index ed0583f9e27512..35baadd130795c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1889,8 +1889,6 @@ void *filemap_get_entry(struct address_space *mapping, pgoff_t index)
  *
  * * %FGP_ACCESSED - The folio will be marked accessed.
  * * %FGP_LOCK - The folio is returned locked.
- * * %FGP_ENTRY - If there is a shadow / swap / DAX entry, return it
- *   instead of allocating a new folio to replace it.
  * * %FGP_CREAT - If no page is present then a new page is allocated using
  *   @gfp and added to the page cache and the VM's LRU list.
  *   The page is returned locked and with an increased refcount.
@@ -1916,11 +1914,8 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 
 repeat:
 	folio = filemap_get_entry(mapping, index);
-	if (xa_is_value(folio)) {
-		if (fgp_flags & FGP_ENTRY)
-			return folio;
+	if (xa_is_value(folio))
 		folio = NULL;
-	}
 	if (!folio)
 		goto no_page;
 
diff --git a/mm/folio-compat.c b/mm/folio-compat.c
index 18c48b55792635..f3841b4977b68e 100644
--- a/mm/folio-compat.c
+++ b/mm/folio-compat.c
@@ -97,8 +97,8 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
 	struct folio *folio;
 
 	folio = __filemap_get_folio(mapping, index, fgp_flags, gfp);
-	if (!folio || xa_is_value(folio))
-		return &folio->page;
+	if (!folio)
+		return NULL;
 	return folio_file_page(folio, index);
 }
 EXPORT_SYMBOL(pagecache_get_page);
-- 
2.39.0

[PATCH 7/7] mm: return an ERR_PTR from __filemap_get_folio

[Christoph Hellwig]

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.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/afs/dir.c             | 10 +++++-----
 fs/afs/dir_edit.c        |  2 +-
 fs/afs/write.c           |  4 ++--
 fs/btrfs/disk-io.c       |  2 +-
 fs/ext4/inode.c          |  2 +-
 fs/ext4/move_extent.c    |  8 ++++----
 fs/hugetlbfs/inode.c     |  2 +-
 fs/iomap/buffered-io.c   | 15 ++-------------
 fs/netfs/buffered_read.c |  4 ++--
 fs/nilfs2/page.c         |  6 +++---
 include/linux/pagemap.h  | 11 ++++++-----
 mm/filemap.c             | 14 ++++++++------
 mm/folio-compat.c        |  2 +-
 mm/huge_memory.c         |  2 +-
 mm/memcontrol.c          |  2 +-
 mm/mincore.c             |  2 +-
 mm/shmem.c               |  4 ++--
 mm/swap_state.c          | 15 ++++++++-------
 mm/swapfile.c            |  4 ++--
 mm/truncate.c            | 15 ++++++++-------
 20 files changed, 60 insertions(+), 66 deletions(-)

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 82690d1dd49a02..f92b9e62d567b9 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -319,16 +319,16 @@ static struct afs_read *afs_read_dir(struct afs_vnode *dvnode, struct key *key)
 		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 0ab7752d1b758e..f0eddccbdd9541 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 2d3b08b7406ca7..cf1eb0d122c275 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/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 27abe8fdfd92b3..e888abee119fd6 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -4037,7 +4037,7 @@ static int wait_dev_supers(struct btrfs_device *device, int max_mirrors)
 
 		folio = filemap_get_folio(device->bdev->bd_inode->i_mapping,
 				     bytenr >> PAGE_SHIFT);
-		if (!folio) {
+		if (IS_ERR(folio)) {
 			errors++;
 			if (i == 0)
 				primary_failed = true;
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 0f6f24bb8e8fba..b4c65e6aa360d2 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5391,7 +5391,7 @@ 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 2de9829aed63bf..7bf6d069199cbb 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 fb810664448787..6cac1b92520af1 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 d3c300563eb8ff..94a4d2e66ac66d 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);
 
@@ -653,10 +646,6 @@ static int iomap_write_begin(struct iomap_iter *iter, loff_t pos,
 	if (!mapping_large_folio_support(iter->inode->i_mapping))
 		len = min_t(size_t, len, PAGE_SIZE - offset_in_page(pos));
 
-	folio = __iomap_get_folio(iter, pos, len);
-	if (IS_ERR(folio))
-		return PTR_ERR(folio);
-
 	/*
 	 * Now we have a locked folio, before we do anything with it we need to
 	 * check that the iomap we have cached is not stale. The inode extent
@@ -911,7 +900,7 @@ 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 7679a68e819307..209726a9cfdb9c 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/nilfs2/page.c b/fs/nilfs2/page.c
index 41ccd43cd9797f..5cf30827f244c4 100644
--- a/fs/nilfs2/page.c
+++ b/fs/nilfs2/page.c
@@ -259,10 +259,10 @@ int nilfs_copy_dirty_pages(struct address_space *dmap,
 			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 @@ void nilfs_copy_back_pages(struct address_space *dmap,
 
 		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);
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index e2208ee36966ea..6e07ba2ef18327 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -520,7 +520,8 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
  * Looks up the page cache entry at @mapping & @index.  If a folio is
  * present, it is returned with an increased refcount.
  *
- * Otherwise, %NULL is returned.
+ * Return: A folio or ERR_PTR(-ENOENT) if there is no folio in the cache for
+ * this index.  Will not return a shadow, swap or DAX entry.
  */
 static inline struct folio *filemap_get_folio(struct address_space *mapping,
 					pgoff_t index)
@@ -537,8 +538,8 @@ static inline struct folio *filemap_get_folio(struct address_space *mapping,
  * present, it is returned locked with an increased refcount.
  *
  * Context: May sleep.
- * Return: A folio or %NULL if there is no folio in the cache for this
- * index.  Will not return a shadow, swap or DAX entry.
+ * Return: A folio or ERR_PTR(-ENOENT) if there is no folio in the cache for
+ * this index.  Will not return a shadow, swap or DAX entry.
  */
 static inline struct folio *filemap_lock_folio(struct address_space *mapping,
 					pgoff_t index)
@@ -555,8 +556,8 @@ static inline struct folio *filemap_lock_folio(struct address_space *mapping,
  * a new folio is created. The folio is locked, marked as accessed, and
  * returned.
  *
- * Return: A found or created folio. NULL if no folio is found and failed to
- * create a folio.
+ * Return: A found or created folio. ERR_PTR(-ENOMEM) if no folio is found
+ * and failed to create a folio.
  */
 static inline struct folio *filemap_grab_folio(struct address_space *mapping,
 					pgoff_t index)
diff --git a/mm/filemap.c b/mm/filemap.c
index 35baadd130795c..4037a132f7adcc 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1905,7 +1905,7 @@ void *filemap_get_entry(struct address_space *mapping, pgoff_t index)
  *
  * If there is a page cache page, it is returned with an increased refcount.
  *
- * Return: The found folio or %NULL otherwise.
+ * Return: The found folio or an ERR_PTR() otherwise.
  */
 struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 		int fgp_flags, gfp_t gfp)
@@ -1923,7 +1923,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 		if (fgp_flags & FGP_NOWAIT) {
 			if (!folio_trylock(folio)) {
 				folio_put(folio);
-				return NULL;
+				return ERR_PTR(-EAGAIN);
 			}
 		} else {
 			folio_lock(folio);
@@ -1962,7 +1962,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 
 		folio = filemap_alloc_folio(gfp, 0);
 		if (!folio)
-			return NULL;
+			return ERR_PTR(-ENOMEM);
 
 		if (WARN_ON_ONCE(!(fgp_flags & (FGP_LOCK | FGP_FOR_MMAP))))
 			fgp_flags |= FGP_LOCK;
@@ -1987,6 +1987,8 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 			folio_unlock(folio);
 	}
 
+	if (!folio)
+		return ERR_PTR(-ENOENT);
 	return folio;
 }
 EXPORT_SYMBOL(__filemap_get_folio);
@@ -3126,7 +3128,7 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 	 * Do we have something in the page cache already?
 	 */
 	folio = filemap_get_folio(mapping, index);
-	if (likely(folio)) {
+	if (likely(!IS_ERR(folio))) {
 		/*
 		 * We found the page, so try async readahead before waiting for
 		 * the lock.
@@ -3155,7 +3157,7 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 		folio = __filemap_get_folio(mapping, index,
 					  FGP_CREAT|FGP_FOR_MMAP,
 					  vmf->gfp_mask);
-		if (!folio) {
+		if (IS_ERR(folio)) {
 			if (fpin)
 				goto out_retry;
 			filemap_invalidate_unlock_shared(mapping);
@@ -3506,7 +3508,7 @@ static struct folio *do_read_cache_folio(struct address_space *mapping,
 		filler = mapping->a_ops->read_folio;
 repeat:
 	folio = filemap_get_folio(mapping, index);
-	if (!folio) {
+	if (IS_ERR(folio)) {
 		folio = filemap_alloc_folio(gfp, 0);
 		if (!folio)
 			return ERR_PTR(-ENOMEM);
diff --git a/mm/folio-compat.c b/mm/folio-compat.c
index f3841b4977b68e..4cd173336d8589 100644
--- a/mm/folio-compat.c
+++ b/mm/folio-compat.c
@@ -97,7 +97,7 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
 	struct folio *folio;
 
 	folio = __filemap_get_folio(mapping, index, fgp_flags, gfp);
-	if (!folio)
+	if (IS_ERR(folio))
 		return NULL;
 	return folio_file_page(folio, index);
 }
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index a2830019aaa017..b0c9170632e37c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3103,7 +3103,7 @@ static int split_huge_pages_in_file(const char *file_path, pgoff_t off_start,
 		struct folio *folio = filemap_get_folio(mapping, index);
 
 		nr_pages = 1;
-		if (!folio)
+		if (IS_ERR(folio))
 			continue;
 
 		if (!folio_test_large(folio))
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 17335459d8dc72..7ecebdd2c23391 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5689,7 +5689,7 @@ static struct page *mc_handle_file_pte(struct vm_area_struct *vma,
 	/* shmem/tmpfs may report page out on swap: account for that too. */
 	index = linear_page_index(vma, addr);
 	folio = filemap_get_incore_folio(vma->vm_file->f_mapping, index);
-	if (!folio)
+	if (IS_ERR(folio))
 		return NULL;
 	return folio_file_page(folio, index);
 }
diff --git a/mm/mincore.c b/mm/mincore.c
index cd69b9db008126..5437e584b208bf 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -61,7 +61,7 @@ static unsigned char mincore_page(struct address_space *mapping, pgoff_t index)
 	 * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
 	 */
 	folio = filemap_get_incore_folio(mapping, index);
-	if (folio) {
+	if (!IS_ERR(folio)) {
 		present = folio_test_uptodate(folio);
 		folio_put(folio);
 	}
diff --git a/mm/shmem.c b/mm/shmem.c
index 23d5cf8182cb1f..8589ab4abd2b11 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -603,7 +603,7 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
 
 		index = (inode->i_size & HPAGE_PMD_MASK) >> PAGE_SHIFT;
 		folio = filemap_get_folio(inode->i_mapping, index);
-		if (!folio)
+		if (IS_ERR(folio))
 			goto drop;
 
 		/* No huge page at the end of the file: nothing to split */
@@ -3187,7 +3187,7 @@ static const char *shmem_get_link(struct dentry *dentry,
 
 	if (!dentry) {
 		folio = filemap_get_folio(inode->i_mapping, 0);
-		if (!folio)
+		if (IS_ERR(folio))
 			return ERR_PTR(-ECHILD);
 		if (PageHWPoison(folio_page(folio, 0)) ||
 		    !folio_test_uptodate(folio)) {
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 92234f4b51d29a..c7160070b9daa9 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;
@@ -389,22 +391,21 @@ struct folio *filemap_get_incore_folio(struct address_space *mapping,
 	struct folio *folio = filemap_get_entry(mapping, index);
 
 	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 +432,7 @@ 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));
 
 		/*
diff --git a/mm/swapfile.c b/mm/swapfile.c
index a5729273480e07..a128b61b6b8c91 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -136,7 +136,7 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si,
 	int ret = 0;
 
 	folio = filemap_get_folio(swap_address_space(entry), offset);
-	if (!folio)
+	if (IS_ERR(folio))
 		return 0;
 	/*
 	 * When this function is called from scan_swap_map_slots() and it's
@@ -2096,7 +2096,7 @@ static int try_to_unuse(unsigned int type)
 
 		entry = swp_entry(type, i);
 		folio = filemap_get_folio(swap_address_space(entry), i);
-		if (!folio)
+		if (IS_ERR(folio))
 			continue;
 
 		/*
diff --git a/mm/truncate.c b/mm/truncate.c
index 7b4ea4c4a46b20..86de31ed4d3238 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;
-- 
2.39.0

Re: [PATCH 7/7] mm: return an ERR_PTR from __filemap_get_folio

[kernel test robot]

Hi Christoph,

I love your patch! Perhaps something to improve:

[auto build test WARNING on next-20230120]
[cannot apply to akpm-mm/mm-everything tytso-ext4/dev kdave/for-next xfs-linux/for-next konis-nilfs2/upstream linus/master v6.2-rc4 v6.2-rc3 v6.2-rc2 v6.2-rc4]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Christoph-Hellwig/mm-make-mapping_get_entry-available-outside-of-filemap-c/20230121-155847
patch link:    https://lore.kernel.org/r/20230121065755.1140136-8-hch%40lst.de
patch subject: [PATCH 7/7] mm: return an ERR_PTR from __filemap_get_folio
config: riscv-randconfig-r013-20230119 (https://download.01.org/0day-ci/archive/20230121/202301211944.5T9l1RgA-lkp@intel.com/config)
compiler: clang version 16.0.0 (https://github.com/llvm/llvm-project 4196ca3278f78c6e19246e54ab0ecb364e37d66a)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install riscv cross compiling tool for clang build
        # apt-get install binutils-riscv-linux-gnu
        # https://github.com/intel-lab-lkp/linux/commit/3c8a98fd03b82ace84668b3f8bb48d48e9f34af2
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Christoph-Hellwig/mm-make-mapping_get_entry-available-outside-of-filemap-c/20230121-155847
        git checkout 3c8a98fd03b82ace84668b3f8bb48d48e9f34af2
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=riscv olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=riscv SHELL=/bin/bash fs/iomap/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> fs/iomap/buffered-io.c:669:28: warning: variable 'folio' is uninitialized when used here [-Wuninitialized]
           if (pos + len > folio_pos(folio) + folio_size(folio))
                                     ^~~~~
   fs/iomap/buffered-io.c:636:21: note: initialize the variable 'folio' to silence this warning
           struct folio *folio;
                              ^
                               = NULL
   fs/iomap/buffered-io.c:598:22: warning: unused function '__iomap_get_folio' [-Wunused-function]
   static struct folio *__iomap_get_folio(struct iomap_iter *iter, loff_t pos,
                        ^
   2 warnings generated.


vim +/folio +669 fs/iomap/buffered-io.c

69f4a26c1e0c7c Gao Xiang               2021-08-03  630  
d7b64041164ca1 Dave Chinner            2022-11-29  631  static int iomap_write_begin(struct iomap_iter *iter, loff_t pos,
bc6123a84a71b5 Matthew Wilcox (Oracle  2021-05-02  632) 		size_t len, struct folio **foliop)
afc51aaa22f26c Darrick J. Wong         2019-07-15  633  {
471859f57d4253 Andreas Gruenbacher     2023-01-15  634  	const struct iomap_folio_ops *folio_ops = iter->iomap.folio_ops;
fad0a1ab34f777 Christoph Hellwig       2021-08-10  635  	const struct iomap *srcmap = iomap_iter_srcmap(iter);
d1bd0b4ebfe052 Matthew Wilcox (Oracle  2021-11-03  636) 	struct folio *folio;
afc51aaa22f26c Darrick J. Wong         2019-07-15  637  	int status = 0;
afc51aaa22f26c Darrick J. Wong         2019-07-15  638  
1b5c1e36dc0e0f Christoph Hellwig       2021-08-10  639  	BUG_ON(pos + len > iter->iomap.offset + iter->iomap.length);
1b5c1e36dc0e0f Christoph Hellwig       2021-08-10  640  	if (srcmap != &iter->iomap)
c039b997927263 Goldwyn Rodrigues       2019-10-18  641  		BUG_ON(pos + len > srcmap->offset + srcmap->length);
afc51aaa22f26c Darrick J. Wong         2019-07-15  642  
afc51aaa22f26c Darrick J. Wong         2019-07-15  643  	if (fatal_signal_pending(current))
afc51aaa22f26c Darrick J. Wong         2019-07-15  644  		return -EINTR;
afc51aaa22f26c Darrick J. Wong         2019-07-15  645  
d454ab82bc7f4a Matthew Wilcox (Oracle  2021-12-09  646) 	if (!mapping_large_folio_support(iter->inode->i_mapping))
d454ab82bc7f4a Matthew Wilcox (Oracle  2021-12-09  647) 		len = min_t(size_t, len, PAGE_SIZE - offset_in_page(pos));
d454ab82bc7f4a Matthew Wilcox (Oracle  2021-12-09  648) 
d7b64041164ca1 Dave Chinner            2022-11-29  649  	/*
d7b64041164ca1 Dave Chinner            2022-11-29  650  	 * Now we have a locked folio, before we do anything with it we need to
d7b64041164ca1 Dave Chinner            2022-11-29  651  	 * check that the iomap we have cached is not stale. The inode extent
d7b64041164ca1 Dave Chinner            2022-11-29  652  	 * mapping can change due to concurrent IO in flight (e.g.
d7b64041164ca1 Dave Chinner            2022-11-29  653  	 * IOMAP_UNWRITTEN state can change and memory reclaim could have
d7b64041164ca1 Dave Chinner            2022-11-29  654  	 * reclaimed a previously partially written page at this index after IO
d7b64041164ca1 Dave Chinner            2022-11-29  655  	 * completion before this write reaches this file offset) and hence we
d7b64041164ca1 Dave Chinner            2022-11-29  656  	 * could do the wrong thing here (zero a page range incorrectly or fail
d7b64041164ca1 Dave Chinner            2022-11-29  657  	 * to zero) and corrupt data.
d7b64041164ca1 Dave Chinner            2022-11-29  658  	 */
471859f57d4253 Andreas Gruenbacher     2023-01-15  659  	if (folio_ops && folio_ops->iomap_valid) {
471859f57d4253 Andreas Gruenbacher     2023-01-15  660  		bool iomap_valid = folio_ops->iomap_valid(iter->inode,
d7b64041164ca1 Dave Chinner            2022-11-29  661  							 &iter->iomap);
d7b64041164ca1 Dave Chinner            2022-11-29  662  		if (!iomap_valid) {
d7b64041164ca1 Dave Chinner            2022-11-29  663  			iter->iomap.flags |= IOMAP_F_STALE;
d7b64041164ca1 Dave Chinner            2022-11-29  664  			status = 0;
d7b64041164ca1 Dave Chinner            2022-11-29  665  			goto out_unlock;
d7b64041164ca1 Dave Chinner            2022-11-29  666  		}
d7b64041164ca1 Dave Chinner            2022-11-29  667  	}
d7b64041164ca1 Dave Chinner            2022-11-29  668  
d454ab82bc7f4a Matthew Wilcox (Oracle  2021-12-09 @669) 	if (pos + len > folio_pos(folio) + folio_size(folio))
d454ab82bc7f4a Matthew Wilcox (Oracle  2021-12-09  670) 		len = folio_pos(folio) + folio_size(folio) - pos;
afc51aaa22f26c Darrick J. Wong         2019-07-15  671  
c039b997927263 Goldwyn Rodrigues       2019-10-18  672  	if (srcmap->type == IOMAP_INLINE)
bc6123a84a71b5 Matthew Wilcox (Oracle  2021-05-02  673) 		status = iomap_write_begin_inline(iter, folio);
1b5c1e36dc0e0f Christoph Hellwig       2021-08-10  674  	else if (srcmap->flags & IOMAP_F_BUFFER_HEAD)
d1bd0b4ebfe052 Matthew Wilcox (Oracle  2021-11-03  675) 		status = __block_write_begin_int(folio, pos, len, NULL, srcmap);
afc51aaa22f26c Darrick J. Wong         2019-07-15  676  	else
bc6123a84a71b5 Matthew Wilcox (Oracle  2021-05-02  677) 		status = __iomap_write_begin(iter, pos, len, folio);
afc51aaa22f26c Darrick J. Wong         2019-07-15  678  
afc51aaa22f26c Darrick J. Wong         2019-07-15  679  	if (unlikely(status))
afc51aaa22f26c Darrick J. Wong         2019-07-15  680  		goto out_unlock;
afc51aaa22f26c Darrick J. Wong         2019-07-15  681  
bc6123a84a71b5 Matthew Wilcox (Oracle  2021-05-02  682) 	*foliop = folio;
afc51aaa22f26c Darrick J. Wong         2019-07-15  683  	return 0;
afc51aaa22f26c Darrick J. Wong         2019-07-15  684  
afc51aaa22f26c Darrick J. Wong         2019-07-15  685  out_unlock:
7a70a5085ed028 Andreas Gruenbacher     2023-01-15  686  	__iomap_put_folio(iter, pos, 0, folio);
1b5c1e36dc0e0f Christoph Hellwig       2021-08-10  687  	iomap_write_failed(iter->inode, pos, len);
afc51aaa22f26c Darrick J. Wong         2019-07-15  688  
afc51aaa22f26c Darrick J. Wong         2019-07-15  689  	return status;
afc51aaa22f26c Darrick J. Wong         2019-07-15  690  }
afc51aaa22f26c Darrick J. Wong         2019-07-15  691  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests

Re: [PATCH 7/7] mm: return an ERR_PTR from __filemap_get_folio

[Christoph Hellwig]

On Sat, Jan 21, 2023 at 07:52:54PM +0800, kernel test robot wrote:
> Hi Christoph,
> 
> I love your patch! Perhaps something to improve:

And I don't love all this hugging when something doesn't work.  It feels
passive aggressive.

That being said, in this case the error is becaue the series is against
linux-next, so applying it to mainline won't work.

Re: [PATCH 7/7] mm: return an ERR_PTR from __filemap_get_folio

[David Sterba]

On Sat, Jan 21, 2023 at 07:57:55AM +0100, Christoph Hellwig wrote:
> 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.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/afs/dir.c             | 10 +++++-----
>  fs/afs/dir_edit.c        |  2 +-
>  fs/afs/write.c           |  4 ++--

For

>  fs/btrfs/disk-io.c       |  2 +-

Acked-by: David Sterba <dsterba@suse.com>

Re: [PATCH 7/7] mm: return an ERR_PTR from __filemap_get_folio

[Ryusuke Konishi]

On Sat, Jan 21, 2023 at 3:59 PM Christoph Hellwig wrote:
>
> 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.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---

For

>  fs/nilfs2/page.c         |  6 +++---

Acked-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>

Thanks,
Ryusuke Konishi

Re: [PATCH 7/7] mm: return an ERR_PTR from __filemap_get_folio

[Naoya Horiguchi]

On Sat, Jan 21, 2023 at 07:57:55AM +0100, Christoph Hellwig wrote:
> 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.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Hello,

I found a NULL pointer dereference issue related to this patch,
so let me share it.

Here is the bug message (I used akpm/mm-unstable on Mar 9):

[ 2871.648659] BUG: kernel NULL pointer dereference, address: 0000000000000000
[ 2871.651286] #PF: supervisor read access in kernel mode
[ 2871.653231] #PF: error_code(0x0000) - not-present page
[ 2871.655170] PGD 80000001517dd067 P4D 80000001517dd067 PUD 1491d1067 PMD 0
[ 2871.657739] Oops: 0000 [#1] PREEMPT SMP PTI
[ 2871.659329] CPU: 4 PID: 1599 Comm: page-types Tainted: G            E    N 6.3.0-rc1-v6.3-rc1-230309-1629-189-ga71a7+ #36
[ 2871.663362] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014
[ 2871.666507] RIP: 0010:mincore_page+0x19/0x90
[ 2871.668086] Code: cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 41 54 55 53 e8 92 2b 03 00 48 3d 00 f0 ff ff 77 54 48 89 c3 <48> 8b 00 48 c1 e8 02 89 c5 83 e5 01 75 21 8b 43 34 85 c0 74 47 f0
[ 2871.678313] RSP: 0018:ffffbe57c203fd00 EFLAGS: 00010207
[ 2871.681422] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
[ 2871.685609] RDX: 0000000000000000 RSI: ffff9f59ca1506d8 RDI: ffff9f59ce7c2880
[ 2871.689599] RBP: 0000000000000000 R08: 00007f9f14200000 R09: ffff9f59c9078508
[ 2871.693295] R10: 00007f9ed4400000 R11: 0000000000000000 R12: 0000000000000200
[ 2871.695969] R13: 0000000000000001 R14: ffff9f59c9ef4450 R15: ffff9f59c4ac9000
[ 2871.699927] FS:  00007f9ed47ee740(0000) GS:ffff9f5abbc00000(0000) knlGS:0000000000000000
[ 2871.703969] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2871.706689] CR2: 0000000000000000 CR3: 0000000149ffe006 CR4: 0000000000170ee0
[ 2871.709923] DR0: ffffffff91531760 DR1: ffffffff91531761 DR2: ffffffff91531762
[ 2871.713424] DR3: ffffffff91531763 DR6: 00000000ffff0ff0 DR7: 0000000000000600
[ 2871.716758] Call Trace:
[ 2871.717998]  <TASK>
[ 2871.719008]  __mincore_unmapped_range+0x6e/0xd0
[ 2871.721220]  mincore_unmapped_range+0x16/0x30
[ 2871.723288]  walk_pgd_range+0x485/0x9e0
[ 2871.725128]  __walk_page_range+0x195/0x1b0
[ 2871.727224]  walk_page_range+0x151/0x180
[ 2871.728883]  __do_sys_mincore+0xec/0x2b0
[ 2871.730707]  do_syscall_64+0x3a/0x90
[ 2871.732179]  entry_SYSCALL_64_after_hwframe+0x72/0xdc
[ 2871.734148] RIP: 0033:0x7f9ed443f4ab
[ 2871.735548] Code: 73 01 c3 48 8b 0d 75 99 1b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 1b 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 45 99 1b 00 f7 d8 64 89 01 48
[ 2871.742194] RSP: 002b:00007ffe924d72b8 EFLAGS: 00000206 ORIG_RAX: 000000000000001b
[ 2871.744787] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f9ed443f4ab
[ 2871.747186] RDX: 00007ffe92557300 RSI: 0000000000200000 RDI: 00007f9ed4200000
[ 2871.749404] RBP: 00007ffe92567330 R08: 0000000000000005 R09: 0000000000000000
[ 2871.751683] R10: 00007f9ed4405d68 R11: 0000000000000206 R12: 00007ffe925674b8
[ 2871.753925] R13: 0000000000404af1 R14: 000000000040ad78 R15: 00007f9ed4833000
[ 2871.756493]  </TASK>

The precedure to reproduce this is (1) punch hole some page in a shmem
file, then (2) call mincore() over the punch-holed address range. 

I confirmed that filemap_get_incore_folio() (actually filemap_get_entry()
inside it) returns NULL in that case, so we unexpectedly enter the following
if-block for the "not found" case.

> diff --git a/mm/mincore.c b/mm/mincore.c
> index cd69b9db008126..5437e584b208bf 100644
> --- a/mm/mincore.c
> +++ b/mm/mincore.c
> @@ -61,7 +61,7 @@ static unsigned char mincore_page(struct address_space *mapping, pgoff_t index)
>  	 * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
>  	 */
>  	folio = filemap_get_incore_folio(mapping, index);
> -	if (folio) {
> +	if (!IS_ERR(folio)) {
>  		present = folio_test_uptodate(folio);
>  		folio_put(folio);
>  	}

I guess that this patch intends to make filemap_get_incore_folio() return
non-NULL error code, so replacing the check with "if (!IS_ERR_OR_NULL(folio))"
cannot be a solution. But I have no idea about the fix, so could you help me?

Thanks,
Naoya Horiguchi

Re: [PATCH 7/7] mm: return an ERR_PTR from __filemap_get_folio

[Christoph Hellwig]

On Fri, Mar 10, 2023 at 01:31:37PM +0900, Naoya Horiguchi wrote:
> On Sat, Jan 21, 2023 at 07:57:55AM +0100, Christoph Hellwig wrote:
> > 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.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> Hello,
> 
> I found a NULL pointer dereference issue related to this patch,
> so let me share it.
> 
> Here is the bug message (I used akpm/mm-unstable on Mar 9):
> 
> [ 2871.648659] BUG: kernel NULL pointer dereference, address: 0000000000000000
> [ 2871.651286] #PF: supervisor read access in kernel mode
> [ 2871.653231] #PF: error_code(0x0000) - not-present page
> [ 2871.655170] PGD 80000001517dd067 P4D 80000001517dd067 PUD 1491d1067 PMD 0
> [ 2871.657739] Oops: 0000 [#1] PREEMPT SMP PTI
> [ 2871.659329] CPU: 4 PID: 1599 Comm: page-types Tainted: G            E    N 6.3.0-rc1-v6.3-rc1-230309-1629-189-ga71a7+ #36
> [ 2871.663362] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014
> [ 2871.666507] RIP: 0010:mincore_page+0x19/0x90
> [ 2871.668086] Code: cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 41 54 55 53 e8 92 2b 03 00 48 3d 00 f0 ff ff 77 54 48 89 c3 <48> 8b 00 48 c1 e8 02 89 c5 83 e5 01 75 21 8b 43 34 85 c0 74 47 f0
> [ 2871.678313] RSP: 0018:ffffbe57c203fd00 EFLAGS: 00010207
> [ 2871.681422] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> [ 2871.685609] RDX: 0000000000000000 RSI: ffff9f59ca1506d8 RDI: ffff9f59ce7c2880
> [ 2871.689599] RBP: 0000000000000000 R08: 00007f9f14200000 R09: ffff9f59c9078508
> [ 2871.693295] R10: 00007f9ed4400000 R11: 0000000000000000 R12: 0000000000000200
> [ 2871.695969] R13: 0000000000000001 R14: ffff9f59c9ef4450 R15: ffff9f59c4ac9000
> [ 2871.699927] FS:  00007f9ed47ee740(0000) GS:ffff9f5abbc00000(0000) knlGS:0000000000000000
> [ 2871.703969] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 2871.706689] CR2: 0000000000000000 CR3: 0000000149ffe006 CR4: 0000000000170ee0
> [ 2871.709923] DR0: ffffffff91531760 DR1: ffffffff91531761 DR2: ffffffff91531762
> [ 2871.713424] DR3: ffffffff91531763 DR6: 00000000ffff0ff0 DR7: 0000000000000600
> [ 2871.716758] Call Trace:
> [ 2871.717998]  <TASK>
> [ 2871.719008]  __mincore_unmapped_range+0x6e/0xd0
> [ 2871.721220]  mincore_unmapped_range+0x16/0x30
> [ 2871.723288]  walk_pgd_range+0x485/0x9e0
> [ 2871.725128]  __walk_page_range+0x195/0x1b0
> [ 2871.727224]  walk_page_range+0x151/0x180
> [ 2871.728883]  __do_sys_mincore+0xec/0x2b0
> [ 2871.730707]  do_syscall_64+0x3a/0x90
> [ 2871.732179]  entry_SYSCALL_64_after_hwframe+0x72/0xdc
> [ 2871.734148] RIP: 0033:0x7f9ed443f4ab
> [ 2871.735548] Code: 73 01 c3 48 8b 0d 75 99 1b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 1b 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 45 99 1b 00 f7 d8 64 89 01 48
> [ 2871.742194] RSP: 002b:00007ffe924d72b8 EFLAGS: 00000206 ORIG_RAX: 000000000000001b
> [ 2871.744787] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f9ed443f4ab
> [ 2871.747186] RDX: 00007ffe92557300 RSI: 0000000000200000 RDI: 00007f9ed4200000
> [ 2871.749404] RBP: 00007ffe92567330 R08: 0000000000000005 R09: 0000000000000000
> [ 2871.751683] R10: 00007f9ed4405d68 R11: 0000000000000206 R12: 00007ffe925674b8
> [ 2871.753925] R13: 0000000000404af1 R14: 000000000040ad78 R15: 00007f9ed4833000
> [ 2871.756493]  </TASK>
> 
> The precedure to reproduce this is (1) punch hole some page in a shmem
> file, then (2) call mincore() over the punch-holed address range. 
> 
> I confirmed that filemap_get_incore_folio() (actually filemap_get_entry()
> inside it) returns NULL in that case, so we unexpectedly enter the following
> if-block for the "not found" case.

Yes.  Please try this fix:

diff --git a/mm/swap_state.c b/mm/swap_state.c
index c7160070b9daa9..b76a65ac28b319 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -390,6 +390,8 @@ 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))
 		return folio;
 	if (!shmem_mapping(mapping))

Re: [PATCH 7/7] mm: return an ERR_PTR from __filemap_get_folio

[Naoya Horiguchi]

On Fri, Mar 10, 2023 at 08:00:23AM +0100, Christoph Hellwig wrote:
> On Fri, Mar 10, 2023 at 01:31:37PM +0900, Naoya Horiguchi wrote:
> > On Sat, Jan 21, 2023 at 07:57:55AM +0100, Christoph Hellwig wrote:
> > > 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.
> > > 
> > > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > 
> > Hello,
> > 
> > I found a NULL pointer dereference issue related to this patch,
> > so let me share it.
> > 
> > Here is the bug message (I used akpm/mm-unstable on Mar 9):
> > 
> > [ 2871.648659] BUG: kernel NULL pointer dereference, address: 0000000000000000
> > [ 2871.651286] #PF: supervisor read access in kernel mode
> > [ 2871.653231] #PF: error_code(0x0000) - not-present page
> > [ 2871.655170] PGD 80000001517dd067 P4D 80000001517dd067 PUD 1491d1067 PMD 0
> > [ 2871.657739] Oops: 0000 [#1] PREEMPT SMP PTI
> > [ 2871.659329] CPU: 4 PID: 1599 Comm: page-types Tainted: G            E    N 6.3.0-rc1-v6.3-rc1-230309-1629-189-ga71a7+ #36
> > [ 2871.663362] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014
> > [ 2871.666507] RIP: 0010:mincore_page+0x19/0x90
> > [ 2871.668086] Code: cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 41 54 55 53 e8 92 2b 03 00 48 3d 00 f0 ff ff 77 54 48 89 c3 <48> 8b 00 48 c1 e8 02 89 c5 83 e5 01 75 21 8b 43 34 85 c0 74 47 f0
> > [ 2871.678313] RSP: 0018:ffffbe57c203fd00 EFLAGS: 00010207
> > [ 2871.681422] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> > [ 2871.685609] RDX: 0000000000000000 RSI: ffff9f59ca1506d8 RDI: ffff9f59ce7c2880
> > [ 2871.689599] RBP: 0000000000000000 R08: 00007f9f14200000 R09: ffff9f59c9078508
> > [ 2871.693295] R10: 00007f9ed4400000 R11: 0000000000000000 R12: 0000000000000200
> > [ 2871.695969] R13: 0000000000000001 R14: ffff9f59c9ef4450 R15: ffff9f59c4ac9000
> > [ 2871.699927] FS:  00007f9ed47ee740(0000) GS:ffff9f5abbc00000(0000) knlGS:0000000000000000
> > [ 2871.703969] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [ 2871.706689] CR2: 0000000000000000 CR3: 0000000149ffe006 CR4: 0000000000170ee0
> > [ 2871.709923] DR0: ffffffff91531760 DR1: ffffffff91531761 DR2: ffffffff91531762
> > [ 2871.713424] DR3: ffffffff91531763 DR6: 00000000ffff0ff0 DR7: 0000000000000600
> > [ 2871.716758] Call Trace:
> > [ 2871.717998]  <TASK>
> > [ 2871.719008]  __mincore_unmapped_range+0x6e/0xd0
> > [ 2871.721220]  mincore_unmapped_range+0x16/0x30
> > [ 2871.723288]  walk_pgd_range+0x485/0x9e0
> > [ 2871.725128]  __walk_page_range+0x195/0x1b0
> > [ 2871.727224]  walk_page_range+0x151/0x180
> > [ 2871.728883]  __do_sys_mincore+0xec/0x2b0
> > [ 2871.730707]  do_syscall_64+0x3a/0x90
> > [ 2871.732179]  entry_SYSCALL_64_after_hwframe+0x72/0xdc
> > [ 2871.734148] RIP: 0033:0x7f9ed443f4ab
> > [ 2871.735548] Code: 73 01 c3 48 8b 0d 75 99 1b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 1b 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 45 99 1b 00 f7 d8 64 89 01 48
> > [ 2871.742194] RSP: 002b:00007ffe924d72b8 EFLAGS: 00000206 ORIG_RAX: 000000000000001b
> > [ 2871.744787] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f9ed443f4ab
> > [ 2871.747186] RDX: 00007ffe92557300 RSI: 0000000000200000 RDI: 00007f9ed4200000
> > [ 2871.749404] RBP: 00007ffe92567330 R08: 0000000000000005 R09: 0000000000000000
> > [ 2871.751683] R10: 00007f9ed4405d68 R11: 0000000000000206 R12: 00007ffe925674b8
> > [ 2871.753925] R13: 0000000000404af1 R14: 000000000040ad78 R15: 00007f9ed4833000
> > [ 2871.756493]  </TASK>
> > 
> > The precedure to reproduce this is (1) punch hole some page in a shmem
> > file, then (2) call mincore() over the punch-holed address range. 
> > 
> > I confirmed that filemap_get_incore_folio() (actually filemap_get_entry()
> > inside it) returns NULL in that case, so we unexpectedly enter the following
> > if-block for the "not found" case.
> 
> Yes.  Please try this fix:
> 
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index c7160070b9daa9..b76a65ac28b319 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -390,6 +390,8 @@ 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))
>  		return folio;
>  	if (!shmem_mapping(mapping))

Confirmed the fix, thank you very much!

- Naoya Horiguchi

Re: return an ERR_PTR from __filemap_get_folio v2

[Andrew Morton]

On Sat, 21 Jan 2023 07:57:48 +0100 Christoph Hellwig <hch@lst.de> wrote:

> Hi all,
> 
> __filemap_get_folio and its wrappers can return NULL for three different
> conditions, which in some cases requires the caller to reverse engineer
> the decision making.  This is fixed by returning an ERR_PTR instead of
> NULL and thus transporting the reason for the failure.  But to make
> that work we first need to ensure that no xa_value special case is
> returned and thus return the FGP_ENTRY flag.  It turns out that flag
> is barely used and can usually be deal with in a better way.
> 
> Note that the shmem patches in here are non-trivial and need some
> careful review and testing.

I'll hide for a while, awaiting that review.  Plus...

> Changes since v1:
>  - drop the patches to check for errors in btrfs and gfs2
>  - document the new calling conventions for the wrappers around
>    __filemap_get_folio
>  - rebased against the iomap changes in latest linux-next

This patchset doesn't apply to fs/btrfs/ because linux-next contains
this 6+ month-old commit:

commit 964688b32d9ada55a7fce2e650d85ef24188f73f                
Author:     Matthew Wilcox (Oracle) <willy@infradead.org>
AuthorDate: Tue May 17 18:03:27 2022 -0400
Commit:     Matthew Wilcox (Oracle) <willy@infradead.org>
CommitDate: Wed Jun 29 08:51:07 2022 -0400

    btrfs: Use a folio in wait_dev_supers()


Matthew, what's the story here?

Re: return an ERR_PTR from __filemap_get_folio v2

[Christoph Hellwig]

On Sat, Jan 21, 2023 at 05:06:41PM -0800, Andrew Morton wrote:
> This patchset doesn't apply to fs/btrfs/ because linux-next contains
> this 6+ month-old commit:

Hmm.  It was literally written against linux-next as of last morning,
which does not have that commit.

Re: return an ERR_PTR from __filemap_get_folio v2

[Andrew Morton]

On Sun, 22 Jan 2023 08:20:06 +0100 Christoph Hellwig <hch@lst.de> wrote:

> On Sat, Jan 21, 2023 at 05:06:41PM -0800, Andrew Morton wrote:
> > This patchset doesn't apply to fs/btrfs/ because linux-next contains
> > this 6+ month-old commit:
> 
> Hmm.  It was literally written against linux-next as of last morning,
> which does not have that commit.

Confused.  According to 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/fs/btrfs/disk-io.c#n4023

it's there today.  wait_dev_supers() has been foliofied.

Re: return an ERR_PTR from __filemap_get_folio v2

[Christoph Hellwig]

On Mon, Jan 23, 2023 at 10:59:45AM -0800, Andrew Morton wrote:
> On Sun, 22 Jan 2023 08:20:06 +0100 Christoph Hellwig <hch@lst.de> wrote:
> 
> > On Sat, Jan 21, 2023 at 05:06:41PM -0800, Andrew Morton wrote:
> > > This patchset doesn't apply to fs/btrfs/ because linux-next contains
> > > this 6+ month-old commit:
> > 
> > Hmm.  It was literally written against linux-next as of last morning,
> > which does not have that commit.
> 
> Confused.  According to 
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/fs/btrfs/disk-io.c#n4023
> 
> it's there today.  wait_dev_supers() has been foliofied.

Yes, it's there now.  But I'm pretty sure it wasn't there when
I did the last rebase.  Weird.

Re: return an ERR_PTR from __filemap_get_folio v2

[Andrew Morton]

On Sat, 21 Jan 2023 07:57:48 +0100 Christoph Hellwig <hch@lst.de> wrote:

> __filemap_get_folio and its wrappers can return NULL for three different
> conditions, which in some cases requires the caller to reverse engineer
> the decision making.  This is fixed by returning an ERR_PTR instead of
> NULL and thus transporting the reason for the failure.  But to make
> that work we first need to ensure that no xa_value special case is
> returned and thus return the FGP_ENTRY flag.  It turns out that flag
> is barely used and can usually be deal with in a better way.
> 
> Note that the shmem patches in here are non-trivial and need some
> careful review and testing.

How are we going with the review and testing.  I assume that
we're now OK on the runtime testing front, but do you feel that
review has been adequate?

Thanks.

Re: return an ERR_PTR from __filemap_get_folio v2

[Christoph Hellwig]

On Tue, Mar 28, 2023 at 04:04:33PM -0700, Andrew Morton wrote:
> > Note that the shmem patches in here are non-trivial and need some
> > careful review and testing.
> 
> How are we going with the review and testing.  I assume that
> we're now OK on the runtime testing front, but do you feel that
> review has been adequate?

Yes, I think we're fine, mostly due to Hugh.  I'm a little sad about
the simplification / descoping from him, but at least we get the main
objective done.  Maybe at some point we can do another pass at
cleaning up the shmem page finding/reading mess.