This patch set addresses several long standing issues:
- Fix emergency thaw (patch 1 through 4) and make some cleanups while at it
(patches 5 and 6).
- Fix nested freezes for superblock-less block devices (patch 7).
- Integrate sb-level/bdev-level fsfreeze and sanitize the fsfreeze API to
avoid perpetual frost in the event of changes in the filesystem namespace
(patch 8 through 13).
- Add infrastructure needed to support dm-initiated freeze of filesystems
spanning several bdevs and actually use it to implement this feature in
btrfs (patch 14 through 16).
- Export freeze state to userspace through mountinfo (patch 17).
---
[1/17] vfs: add __iterate_supers() and helpers around it
[2/17] fsfreeze: add unlocked version of thaw_super
Preparatory patches to fix s_umount lockup of emergency thaw code.
[3/17] fsfreeze: fix emergency thaw infinite loop
Fix thaw_bdev so that it propagates the error code properly to the caller.
This bug caused emergency thaw to loop infinitely. This is a forward port of
a previous patch by Dave Chinner.
[4/17] fsfreeze: emergency thaw will deadlock on s_umount
Avoid emergency thaw deadlock on s_umount by using unlocked version of
thaw_super() and __iterate_supers() (introduced in patches 2 and 1
respectively).
[5/17] xfs: switch to using super methods for fsfreeze
[6/17] fsfreeze: move emergency thaw code to fs/super.c
Two cleanups (based on previous patches by David Chinner): convert xfs to using
superblock methods for fsfreeze and move emergency thaw code to where it
belongs.
[7/17] fsfreeze: fix nested freezing of sb-less bdevs
Get nested freezes working for sb-less bdevs.
[8/17] fsfreeze: allow bdev level thaws when the sb is unfrozen
[9/17] fsfreeze: freeze_super and thaw_bdev don't play well together
Restore the re-entrancy guards in sb-level API as the first step to achieve
proper sb-level/bdev-level fsfreeze integration.
[10/17] fsfreeze: automatically thaw on umount
The fsfreeze ioctls are a sb-level API which means that to thaw a frozen
filesystem it is necessary to have it in our filesystem hierarchy. To avoid
being stuck with a frozen filesystem and frozen processes by accident, we
automatically thaw filesystems on sys_umount().
[11/17] fsfreeze: add thaw_super_force
Both emergecy thaw and the umount-time automatic thaw need to make sure that
the thaw operation does not fail so with some code refactoring we can share
and clean up the code.
[12/17] fsfreeze: sb-level/bdev-level fsfreeze integration
[13/17] fsfreeze: unfreeze bdevs in addition to filesystems during emergency thaw
Fix the problem that a filesystem frozen through the bdev level API can be
thawed using the superblock level API and make sure that their respective
freeze counters are always consistent with each other.
[14/17] vfs: leverage bd_super in get_super and get_active_super
[15/17] btrfs: store pointer to superblock in bd_super
[16/17] fsfreeze: allow freeze counter lock nesting
Leverage bd_super in get_active_super to be able to get the superblock from the bdev when the filesystem spans several bdevs. Once this is in place, getting
thaw_bdev(), i.e. dm snapshot, and btrfs to play well together is just a matter
of using bd_super in btrfs.
[17/17] fsfreeze: export freeze_count through mountinfo
Export freeze_count through mountinfo so that we have a way to figure out the
current freeze state from userspace.
---
Changes since: v5:
- Fix patch 4 ("fsfreeze: emergency thaw will deadlock on s_umount").
- Add Jan Kara's Reviewed-by to patch 9 ("fsfreeze: freeze_super and
thaw_bdev don't play well together").
- Exclude conflictive check ioctls from the patch set (could be back in a
follow-up patch set) and add a patch to export freeze state to userspace
through mountinfo.
- Add fix for nested freezing of sb-less bdevs.
- Rewrite the patches to integrate sb-level/bdev-level fsfreeze and sanitize
the fsfreeze API (including automatical thawing of filesystems on umount).
- Add infrastructure needed to support dm-initiated freeze of filesystems
spanning several bdevs and actually use it to implement this feature in
btrfs.
Changes since v4:
- Make implementation of iterate_supers_read and iterate_supers_write
symmetric and update locking of emergency thaw code accordingly.
- Add Jan Kara's Reviewed-by to patch 2.
- Add explanation about the change from a block device based emergency thaw
to a superblock based one to patch 4.
- Modify patch 7 so that the new superblock based emergency does not leave
the block device level fsfreeze counter in an inconsistent state.
- Update and comment handling of fsfreeze during mount.
Changes since v3:
- Include right version of the emergency thaw fix (thanks go to Josef for the
heads up).
- Add iterate_supers_(read/write) helpers as suggested by Eric Sandeen.
- Fix typos.
- Add Eric Sandeen's Reviewed-by to patches 2 and 3.
Changes since v2:
- Rebase on top of Jan Kara's patch set which made it upstream.
- Do without the horrible "emergency" parameter as suggested by Jan Kara.
- New approach to fix emergency thaw deadlock on s_umount which does locking
properly.
Changes since v1:
- Do not break unfreezing of block devices without a mounted filesystem.
- Avoid conditional locking in thaw_bdev.
- Update filesystem locking documentation.
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