[00/13] Allow readpage to return a locked page

Message

Matthew Wilcox Sept. 17, 2020, 3:10 p.m. UTC

Linus recently made the page lock more fair.  That means that the old
pattern where we returned from ->readpage with the page unlocked and
then attempted to re-lock it will send us to the back of the queue for
this page's lock.

Ideally all filesystems would return from ->readpage with the
page Uptodate and Locked, but it's a bit painful to convert all the
asynchronous readpage implementations to synchronous.  These ones are
already synchronous, so convert them while I work on iomap.

A further benefit is that a synchronous readpage implementation allows
us to return an error to someone who might actually care about it.
There's no need to SetPageError, but I don't want to learn about how
a dozen filesystems handle I/O errors (hint: they're all different),
so I have not attempted to change that.

Please review your filesystem carefully.  I've tried to catch all the
places where a filesystem calls its own internal readpage implementation
without going through ->readpage, but I may have missed some.

Matthew Wilcox (Oracle) (13):
  mm: Add AOP_UPDATED_PAGE return value
  9p: Tell the VFS that readpage was synchronous
  afs: Tell the VFS that readpage was synchronous
  ceph: Tell the VFS that readpage was synchronous
  cifs: Tell the VFS that readpage was synchronous
  cramfs: Tell the VFS that readpage was synchronous
  ecryptfs: Tell the VFS that readpage was synchronous
  fuse: Tell the VFS that readpage was synchronous
  hostfs: Tell the VFS that readpage was synchronous
  jffs2: Tell the VFS that readpage was synchronous
  ubifs: Tell the VFS that readpage was synchronous
  udf: Tell the VFS that readpage was synchronous
  vboxsf: Tell the VFS that readpage was synchronous

 Documentation/filesystems/locking.rst |  7 ++++---
 Documentation/filesystems/vfs.rst     | 21 ++++++++++++++-------
 fs/9p/vfs_addr.c                      |  6 +++++-
 fs/afs/file.c                         |  3 ++-
 fs/ceph/addr.c                        |  9 +++++----
 fs/cifs/file.c                        |  8 ++++++--
 fs/cramfs/inode.c                     |  5 ++---
 fs/ecryptfs/mmap.c                    | 11 ++++++-----
 fs/fuse/file.c                        |  2 ++
 fs/hostfs/hostfs_kern.c               |  2 ++
 fs/jffs2/file.c                       |  6 ++++--
 fs/ubifs/file.c                       | 16 ++++++++++------
 fs/udf/file.c                         |  3 +--
 fs/vboxsf/file.c                      |  2 ++
 include/linux/fs.h                    |  5 +++++
 mm/filemap.c                          | 12 ++++++++++--
 16 files changed, 80 insertions(+), 38 deletions(-)