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

Matthew Wilcox (Oracle)
2020-09-17T15:13:00Z

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(-)