[PATCH 0/3] super: allow waiting without s_umount held

[Christian Brauner <brauner@kernel.org>]

Hey everyone,

This is an attempty to allow concurrent mounters and iterators to wait
on superblock state changes without having to hold s_umount. This is
made necessary by recent attempts to open block devices after superblock
creation and fixing deadlocks due to blkdev_put() trying to acquire
s_umount while s_umount is already held.

This is on top of Jan's and Christoph's work in vfs.super. Obviously not
for v6.6. I guess this is in between an RFC and meaning it. I hope I got
it right but this is intricate. 

It reliably survives xfstests for btrfs, ext4, and xfs while
concurrently having 7 processes running ustat() hammering on
@super_blocks and a while true loop that tries to mount a filsystem with
an invalid superblock hammering on sget{_fc}() concurrently as well.

Thanks and don't hit me over the head with things.
Christian

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
Christian Brauner (3):
      super: use super_{lock,unlock}()
      super: wait for nascent superblocks
      super: wait until we passed kill super

 fs/super.c         | 327 ++++++++++++++++++++++++++++++++++++++++++-----------
 include/linux/fs.h |   2 +
 2 files changed, 261 insertions(+), 68 deletions(-)
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base-commit: f3aeab61fb15edef1e81828da8dbf0814541e49b
change-id: 20230816-vfs-super-fixes-v3-f2cff6192a50