Re: [PATCH 00/11] fs: use freeze_fs on suspend/hibernate

From: Rafael J. Wysocki
Date: Tue Dec 12 2017 - 20:10:41 EST


On Thursday, November 30, 2017 12:23:45 AM CET Luis R. Rodriguez wrote:
> This is a followup from the original RFC which proposed to start
> to kill kthread freezing all together [0]. Instead of going straight
> out to the jugular for kthread freezing this series only addresses
> killing freezer calls on filesystems which implement freeze_fs, after
> we let the kernel freeze these filesystems for us on suspend.
>
> This approach puts on a slow but steady path towards the original goal
> though. Each subsystem could look for similar solutions. Even with
> filesystems we're not all done yet, after this we'll still have to
> decide what to do about filesystems which do not implement freeze_fs().
>
> Motivation and problem:
>
> kthreads have some semantics for freezing, which helps the kernel
> freeze them when a system is going to suspend or hibernation. These
> semantics are not well defined though, and it actually turns out
> pretty hard to get it right.
>
> Without a proper solution suspend and hibernation are fragile on filesystems,
> it can easily break suspend and fixing such issues are in no way trivial [1]
> [2].
>
> Proposed solution:
>
> Instead of fixing such semantics and trying to get all filesystems to do it
> right, we can easily do away with all freezing calls if the filesystem
> implements a proper freeze_fs() callback. The following 9 filesystems have
> freeze_fs() implemented as such we can let the kernel issue the callback upon
> suspend and thaw on resume automatically on our behalf.
>
> o xfs
> o reiserfs
> o nilfs2
> o jfs
> o f2fs
> o ext4
> o ext2
> o btrfs
>
> Of these, the following have freezer helpers, which can then be removed
> after the kernel automaticaly calls freeze_fs for us on suspend:
>
> o xfs
> o nilfs2
> o jfs
> o f2fs
> o ext4
>
> I've tested this on a system with ext4 and XFS, and have let 0-day go at
> without issues. I have branches availabe for linux-next [3] and Linus'
> latest tree [4].
>
> Further testing, thoughts, reviews, flames are all equally appreciated.
>
> [0] https://lkml.kernel.org/r/20171003185313.1017-1-mcgrof@xxxxxxxxxx
> [1] https://bugzilla.suse.com/show_bug.cgi?id=1043449
> [2] https://lkml.kernel.org/r/20171113103139.GA18936@xxxxxxxxxxxxxxxxxxxx
> [3] https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux-next.git/log/?h=20171129-fs-freeze-cleanup
> [4] https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux.git/log/?h=20171129-fs-freeze-cleanup
>
> Luis R. Rodriguez (11):
> fs: provide unlocked helper for freeze_super()
> fs: provide unlocked helper thaw_super()
> 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: freeze on suspend and thaw on resume
> xfs: remove not needed freezing calls
> ext4: remove not needed freezing calls
> f2fs: remove not needed freezing calls
> nilfs2: remove not needed freezing calls
> jfs: remove not needed freezing calls
>
> fs/ext4/ext4_jbd2.c | 2 +-
> fs/ext4/super.c | 2 -
> fs/f2fs/gc.c | 5 +-
> fs/f2fs/segment.c | 6 +-
> fs/jfs/jfs_logmgr.c | 11 +-
> fs/jfs/jfs_txnmgr.c | 31 ++---
> fs/nilfs2/segment.c | 48 ++++----
> fs/super.c | 320 ++++++++++++++++++++++++++++++++++++++++---------
> fs/xfs/xfs_trans.c | 2 +-
> fs/xfs/xfs_trans_ail.c | 7 +-
> include/linux/fs.h | 63 +++++++++-
> kernel/power/process.c | 15 ++-
> 12 files changed, 378 insertions(+), 134 deletions(-)
>

I'm assuming an update of this to be posted due to the comments from Jan
on patch [3/11] and patch [7/11] probably.

Is there anything else that needs to be addressed?

Thanks,
Rafael