linux-kernel - Re: [PATCH 00/11] fs: use freeze

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Date:   Wed, 13 Dec 2017 02:09:49 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     viro@...iv.linux.org.uk, bart.vanassche@....com,
        ming.lei@...hat.com, tytso@....edu, darrick.wong@...cle.com,
        jikos@...nel.org, pavel@....cz, len.brown@...el.com,
        linux-fsdevel@...r.kernel.org, boris.ostrovsky@...cle.com,
        jgross@...e.com, todd.e.brandt@...ux.intel.com, nborisov@...e.com,
        jack@...e.cz, martin.petersen@...cle.com, ONeukum@...e.com,
        oleksandr@...alenko.name, oleg.b.antonyan@...il.com,
        yu.chen.surf@...il.com, dan.j.williams@...el.com,
        linux-pm@...r.kernel.org, linux-block@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/11] fs: use freeze_fs on suspend/hibernate

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@kernel.org
> [1] https://bugzilla.suse.com/show_bug.cgi?id=1043449
> [2] https://lkml.kernel.org/r/20171113103139.GA18936@yu-chen.sh.intel.com
> [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