linux-kernel - [RFC PATCH 0/4] vfs freeze/thaw on suspend/resume

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Message-ID: <20250327140613.25178-1-James.Bottomley@HansenPartnership.com>
Date: Thu, 27 Mar 2025 10:06:09 -0400
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: mcgrof@...nel.org,
	jack@...e.cz,
	hch@...radead.org,
	david@...morbit.com,
	rafael@...nel.org,
	djwong@...nel.org,
	pavel@...nel.org,
	peterz@...radead.org,
	mingo@...hat.com,
	will@...nel.org,
	boqun.feng@...il.com
Subject: [RFC PATCH 0/4] vfs freeze/thaw on suspend/resume

This sequence is posted as an RFC because it needs to be combined with
Luis' patch set:

https://lore.kernel.org/linux-fsdevel/20250326112220.1988619-1-mcgrof@kernel.org/

In particular I've done nothing to replace the kthread freezing in
filesystems.  I can say that this works flawlessly on 6.14 with my
limited test rig (I only have access to my laptop while at LSF/MM).
My test VM is ext4 root with a file on the root attached to a loop
device and mounted (to test nesting) while running a fio workload on
the upper ext4.

The rwsem rework is absolutely necessary because without it hibernate
immediately fails because systemd-journald tries to record the kernel
messages and gets blocked in sb_start_write() on TASK_INTERRUPTIBLE
which inhibits hibernation.

My goal in doing this is to be able to add a thaw_super() callback to
efivarfs and remove our deadlock prone pm notifier.

Regards,

James

---

James Bottomley (4):
  locking/percpu-rwsem: add freezable alternative to down_read
  vfs: make sb_start_write freezable
  fs/super.c: introduce reverse superblock iterator and use it in
    emergency remount
  vfs: add filesystem freeze/thaw callbacks for power management

 fs/super.c                    | 109 ++++++++++++++++++++++++++++------
 include/linux/fs.h            |   8 ++-
 include/linux/percpu-rwsem.h  |  20 +++++--
 kernel/locking/percpu-rwsem.c |  13 ++--
 kernel/power/hibernate.c      |  12 ++++
 kernel/power/suspend.c        |   4 ++
 6 files changed, 137 insertions(+), 29 deletions(-)

-- 
2.43.0