2023-01-21 07:00:54

by Christoph Hellwig

[permalink] [raw]
Subject: return an ERR_PTR from __filemap_get_folio v2

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(-)


2023-01-22 01:24:28

by Andrew Morton

[permalink] [raw]
Subject: Re: return an ERR_PTR from __filemap_get_folio v2

On Sat, 21 Jan 2023 07:57:48 +0100 Christoph Hellwig <[email protected]> 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) <[email protected]>
AuthorDate: Tue May 17 18:03:27 2022 -0400
Commit: Matthew Wilcox (Oracle) <[email protected]>
CommitDate: Wed Jun 29 08:51:07 2022 -0400

btrfs: Use a folio in wait_dev_supers()


Matthew, what's the story here?

2023-01-22 07:30:14

by Christoph Hellwig

[permalink] [raw]
Subject: Re: return an ERR_PTR from __filemap_get_folio v2

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.