[RFC,0/6] fs: automatic kernel fs freeze / thaw

Message

Luis Chamberlain March 26, 2025, 11:22 a.m. UTC

Based on discussions at LSFMM, on where are we at with automatic fs
suspend / resume. I did a quick check and most of the complexities from
the last series I tried from 2023-03 [0] are now resolved, namely the
following patches are no longer needed as Christian did the work for
this already:

  fs: unify locking semantics for fs freeze / thaw
  fs: distinguish between user initiated freeze and kernel  initiated freeze
  fs: move !SB_BORN check early on freeze and add for thaw

So the only thing left to do is add an fs flag for a sanity check that
the fs doesn't use rely on ktrhead freezing, and enable it for
filesystems which have done that work. This adds the work for
a few filesystems. If regressions are found we can simply remove
FS_AUTOFREEZE from the fs.

I did a quick boot test with this on my laptop and suspend doesn't work,
its not clear if this was an artifact of me trying this on linux-next or
what, I can try without my patches on next to see if next actually
suspends without them. And so, we gotta figure out if there's something
stupid still to fix, or something broken with these changes I overlooked
on the rebase.

[0] https://web.git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux-next.git/log/?h=20230507-fs-freeze

Luis Chamberlain (6):
  fs: add frozen sb state helpers
  fs: add iterate_supers_excl() and iterate_supers_reverse_excl()
  fs: add automatic kernel fs freeze / thaw and remove kthread freezing
  ext4: replace kthread freezing with auto fs freezing
  btrfs: replace kthread freezing with auto fs freezing
  xfs: replace kthread freezing with auto fs freezing

 fs/btrfs/disk-io.c     |   4 +-
 fs/btrfs/scrub.c       |   2 +-
 fs/btrfs/super.c       |   2 +-
 fs/ext4/ext4_jbd2.c    |   2 +-
 fs/ext4/mballoc.c      |   2 +-
 fs/ext4/super.c        |   9 +--
 fs/gfs2/sys.c          |   2 +-
 fs/quota/quota.c       |   3 +-
 fs/super.c             | 149 +++++++++++++++++++++++++++++++++++++++--
 fs/xfs/xfs_discard.c   |   2 +-
 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     |  16 ++---
 fs/xfs/xfs_trans.c     |   3 +-
 fs/xfs/xfs_trans_ail.c |   3 -
 fs/xfs/xfs_zone_gc.c   |   2 -
 include/linux/fs.h     |  38 +++++++++++
 kernel/power/process.c |  15 ++++-
 20 files changed, 223 insertions(+), 40 deletions(-)

Comments

Luis Chamberlain March 26, 2025, 11:42 a.m. UTC | #1

On Wed, Mar 26, 2025 at 04:22:14AM -0700, Luis Chamberlain wrote:
> I did a quick boot test with this on my laptop and suspend doesn't work,
> its not clear if this was an artifact of me trying this on linux-next or
> what, I can try without my patches on next to see if next actually
> suspends without them. And so, we gotta figure out if there's something
> stupid still to fix, or something broken with these changes I overlooked
> on the rebase.

next-20250321 has suspend broken, so it was not my patches which broke
suspend. So we need baseline first on a kernel revision where it is not
broken.

  Luis

James Bottomley March 26, 2025, 12:27 p.m. UTC | #2

On Wed, 2025-03-26 at 04:42 -0700, Luis Chamberlain wrote:
> On Wed, Mar 26, 2025 at 04:22:14AM -0700, Luis Chamberlain wrote:
> > I did a quick boot test with this on my laptop and suspend doesn't
> > work, its not clear if this was an artifact of me trying this on
> > linux-next or what, I can try without my patches on next to see if
> > next actually suspends without them. And so, we gotta figure out if
> > there's something stupid still to fix, or something broken with
> > these changes I overlooked on the rebase.
> 
> next-20250321 has suspend broken, so it was not my patches which
> broke suspend. So we need baseline first on a kernel revision where
> it is not broken.

I wrote a much lighter weight version of this and tested it on 6.14 (or
actually 6.14-rc6 since my laptop takes ages to do a full kernel
compile), which is where I found the sb_write_started() deadlock Jan
predicted.  But with that fixed, at least hibernate works for me using
an ext4 based image, so if you use 6.14 as your base, it should work
for you.

Regards,

James