[PATCH 0/5] super: rework super_lock()

[Christian Brauner <brauner@kernel.org>]

Josef's two series (cf. [1], [2]) left us with four ways to lock a
superblock and two ways to wait for one that's being shut down.
super_lock(), super_lock_shared() and super_lock_excl() return true on
success while super_lock_killable() returns 0. And callers that need an
unmount to be over pair super_lock() with super_wait_shutdown() or
super_wait_shutdown_killable() and have to pick the one that matches
the lock they took. Jan pointed out the bool vs int mess (cf. [3]).

So fold it all into a single super_lock() that takes SUPER_LOCK_EXCL,
SUPER_LOCK_KILLABLE and SUPER_LOCK_WAIT_SHUTDOWN and returns 0 with
s_umount held or a negative error code. The first three patches don't
change behavior.

The fourth patch makes sync(2) killable while it waits for s_umount of
a live superblock. Right now a freeze or remount that's stuck under
s_umount hangs every sync(2) on the machine and nobody can kill it.
fs_bdev_sync() already works that way.

The last patch adds a guard for super_lock() for the callers that take
and drop s_umount in the same scope.

This sits on top of vfs-7.5.super which carries Josef's series.

[1]: https://lore.kernel.org/20261021-b4-super-lock-dying-v1-0-2b35e86706ff@toxicpanda.com
[2]: https://lore.kernel.org/20261021-b4-super-lock-unborn-v1-0-0265eddb6dee@toxicpanda.com
[3]: https://lore.kernel.org/tmw22jj2hn6g6lklme2j3rsfjvmstzpoicvibvmmv6sivd66oj@nhc4lng25gti

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
Christian Brauner (5):
      super: add super_wait()
      super: let super_lock() take flags
      super: let super_lock() wait for a superblock being shut down
      super: make sync(2)'s wait for s_umount killable
      super: add a guard for super_lock()

 fs/super.c | 340 ++++++++++++++++++++++++++++---------------------------------
 1 file changed, 156 insertions(+), 184 deletions(-)
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base-commit: e6d8f4efc8e2301e15de7bcf9e8d3a2134fb058a
change-id: 20261023-work-super-lock_helpers-23d8d257c1b4