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Subject[RFC v3 00/24] vfs: provide automatic kernel freeze / resume
Date
Darrick J. Wong poked me about the status of the fs freez work, he's
right, it's been too long since the last spin. The last v2 attempt happened
in April 2021 [0], this just takes the feedback from Christoph and spins it
again. I've only done basic build tests on x86_64, and haven't yet run time
tested the stuff, but given the size of this set its better to review early
before getting stuck on details. So this is what I've ended up with so far.

Please help me paint the bike shed, and figure out the stuff perhaps
I had not considered yet. The locking stuff is really the important thing
here.

I'd like to re-iterate that tons of areas of the kernel are using the
kthread freezer stuff for things it probably has no reason to use it, so
once we remove this from the fs, it should be easy to start trimming this
from other parts of the kernel. The kthread freezer stuff was put in place
originally stop IO in flight for fs. Other parts of the kernels should
have no business using this stuff after all this work is done.

[0] https://lore.kernel.org/all/20210417001026.23858-1-mcgrof@kernel.org/

Changes since the last v2:
* instead of having different semantics for lock / unlocked freeze
and thaw calls, this unifies the semantics by requiring the lock
prior to freeze / thaw
* uses grab_active_super() now in all all places which need to freeze
or thaw, this includes filesystems, this is to match the locking
requirements, and so to not add new heuristics over defining if the
superblock might be in a good state for freeze/thaw.
* drops SB_FREEZE_COMPLETE_AUTO in favor of just checking for a flag
to be able to determine if userspace initiated the freeze or if its
auto (by the kernel pm)
* folded the pm calls for the VFS so that instead of one call which
has a one-liner with two routines, we use the same one-liner on the
pm side of things.
* split the FS stuff by using a enw temporary flag, so to enable
easier review of the FS changes
* more filesystems use the freezer API now so this also converts them
over
* adjusted the coccinelle rule to use the new flag and in the end
removes it

This is all here too:

https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux-next.git/log/?h=20231010-fs-freeze-v5

Luis Chamberlain (24):
fs: unify locking semantics for fs freeze / thaw
fs: add frozen sb state helpers
fs: distinguish between user initiated freeze and kernel initiated
freeze
fs: add iterate_supers_excl() and iterate_supers_reverse_excl()
fs: add automatic kernel fs freeze / thaw and remove kthread freezing
xfs: replace kthread freezing with auto fs freezing
btrfs: replace kthread freezing with auto fs freezing
ext4: replace kthread freezing with auto fs freezing
f2fs: replace kthread freezing with auto fs freezing
cifs: replace kthread freezing with auto fs freezing
gfs2: replace kthread freezing with auto fs freezing
jfs: replace kthread freezing with auto fs freezing
nilfs2: replace kthread freezing with auto fs freezing
nfs: replace kthread freezing with auto fs freezing
nfsd: replace kthread freezing with auto fs freezing
ubifs: replace kthread freezing with auto fs freezing
ksmbd: replace kthread freezing with auto fs freezing
jffs2: replace kthread freezing with auto fs freezing
jbd2: replace kthread freezing with auto fs freezing
coredump: drop freezer usage
ecryptfs: replace kthread freezing with auto fs freezing
fscache: replace kthread freezing with auto fs freezing
lockd: replace kthread freezing with auto fs freezing
fs: remove FS_AUTOFREEZE

block/bdev.c | 9 +-
fs/btrfs/disk-io.c | 4 +-
fs/btrfs/scrub.c | 2 +-
fs/cifs/cifsfs.c | 10 +-
fs/cifs/connect.c | 8 --
fs/cifs/dfs_cache.c | 2 +-
fs/coredump.c | 2 +-
fs/ecryptfs/kthread.c | 1 -
fs/ext4/ext4_jbd2.c | 2 +-
fs/ext4/super.c | 3 -
fs/f2fs/gc.c | 12 +-
fs/f2fs/segment.c | 6 +-
fs/fscache/main.c | 2 +-
fs/gfs2/glock.c | 6 +-
fs/gfs2/glops.c | 2 +-
fs/gfs2/log.c | 2 -
fs/gfs2/main.c | 4 +-
fs/gfs2/quota.c | 2 -
fs/gfs2/super.c | 11 +-
fs/gfs2/sys.c | 12 +-
fs/gfs2/util.c | 7 +-
fs/ioctl.c | 14 ++-
fs/jbd2/journal.c | 54 ++++-----
fs/jffs2/background.c | 3 +-
fs/jfs/jfs_logmgr.c | 11 +-
fs/jfs/jfs_txnmgr.c | 31 ++----
fs/ksmbd/connection.c | 3 -
fs/ksmbd/transport_tcp.c | 2 -
fs/lockd/clntproc.c | 1 -
fs/lockd/svc.c | 3 -
fs/nfs/callback.c | 4 -
fs/nfsd/nfssvc.c | 2 -
fs/nilfs2/segment.c | 48 ++++----
fs/quota/quota.c | 4 +-
fs/super.c | 232 ++++++++++++++++++++++++++++++++-------
fs/ubifs/commit.c | 4 -
fs/xfs/xfs_log.c | 3 +-
fs/xfs/xfs_log_cil.c | 2 +-
fs/xfs/xfs_mru_cache.c | 2 +-
fs/xfs/xfs_pwork.c | 2 +-
fs/xfs/xfs_super.c | 14 +--
fs/xfs/xfs_trans.c | 3 +-
fs/xfs/xfs_trans_ail.c | 3 -
include/linux/fs.h | 53 ++++++++-
kernel/power/process.c | 15 ++-
45 files changed, 393 insertions(+), 229 deletions(-)

--
2.35.1

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