[git pull][6.17] vfs.git 1/9: d_flags pile

[Al Viro <viro@zeniv.linux.org.uk>]

[trivial conflict in Documentation/filesystems/porting.rst]

The following changes since commit 19272b37aa4f83ca52bdf9c16d5d81bdd1354494:

  Linux 6.16-rc1 (2025-06-08 13:44:43 -0700)

are available in the Git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git tags/pull-dcache

for you to fetch changes up to a509e7cf622bc7ce3f45b1c7047fc2a5e9bea869:

  configfs: use DCACHE_DONTCACHE (2025-06-11 13:41:05 -0400)

----------------------------------------------------------------
	Current exclusion rules for ->d_flags stores are rather unpleasant.
The basic rules are simple:
	* stores to dentry->d_flags are OK under dentry->d_lock.
	* stores to dentry->d_flags are OK in the dentry constructor, before
becomes potentially visible to other threads.
Unfortunately, there's a couple of exceptions to that, and that's where the
headache comes from.

	Main PITA comes from d_set_d_op(); that primitive sets ->d_op
of dentry and adjusts the flags that correspond to presence of individual
methods.  It's very easy to misuse; existing uses _are_ safe, but proof
of correctness is brittle.

	Use in __d_alloc() is safe (we are within a constructor), but we
might as well precalculate the initial value of ->d_flags when we set
the default ->d_op for given superblock and set ->d_flags directly
instead of messing with that helper.

	The reasons why other uses are safe are bloody convoluted; I'm not going
to reproduce it here.  See https://lore.kernel.org/all/20250224010624.GT1977892@ZenIV/
for gory details, if you care.  The critical part is using d_set_d_op() only
just prior to d_splice_alias(), which makes a combination of d_splice_alias()
with setting ->d_op, etc. a natural replacement primitive.  Better yet, if
we go that way, it's easy to take setting ->d_op and modifying ->d_flags
under ->d_lock, which eliminates the headache as far as ->d_flags exclusion
rules are concerned.  Other exceptions are minor and easy to deal with.

	What this series does:
* d_set_d_op() is no longer available; new primitive (d_splice_alias_ops())
is provided, equivalent to combination of d_set_d_op() and d_splice_alias().
* new field of struct super_block - ->s_d_flags.  Default value of ->d_flags
to be used when allocating dentries on this filesystem.
* new primitive for setting ->s_d_op: set_default_d_op().  Replaces stores
to ->s_d_op at mount time.  All in-tree filesystems converted; out-of-tree
ones will get caught by compiler (->s_d_op is renamed, so stores to it will
be caught).  ->s_d_flags is set by the same primitive to match the ->s_d_op.
* a lot of filesystems had ->s_d_op->d_delete equal to always_delete_dentry;
that is equivalent to setting DCACHE_DONTCACHE in ->d_flags, so such filesystems
can bloody well set that bit in ->s_d_flags and drop ->d_delete() from
dentry_operations.  In quite a few cases that results in empty dentry_operations,
which means that we can get rid of those.
* kill simple_dentry_operations - not needed anymore.
* massage d_alloc_parallel() to get rid of the other exception wrt ->d_flags
stores - we can set DCACHE_PAR_LOOKUP as soon as we allocate the new dentry;
no need to delay that until we commit to using the sucker.

As the result, ->d_flags stores are all either under ->d_lock or done before
the dentry becomes visible in any shared data structures.

----------------------------------------------------------------
Al Viro (20):
      d_set_mounted(): we don't need to bump seqcount component of rename_lock
      procfs: kill ->proc_dops
      new helper: d_splice_alias_ops()
      switch procfs from d_set_d_op() to d_splice_alias_ops()
      fuse: no need for special dentry_operations for root dentry
      new helper: set_default_d_op()
      split d_flags calculation out of d_set_d_op()
      correct the set of flags forbidden at d_set_d_op() time
      set_default_d_op(): calculate the matching value for ->d_flags
      simple_lookup(): just set DCACHE_DONTCACHE
      make d_set_d_op() static
      d_alloc_parallel(): set DCACHE_PAR_LOOKUP earlier
      shmem: no dentry retention past the refcount reaching zero
      devpts, sunrpc, hostfs: don't bother with ->d_op
      kill simple_dentry_operations
      ramfs, hugetlbfs, mqueue: set DCACHE_DONTCACHE
      9p: don't bother with always_delete_dentry
      efivarfs: use DCACHE_DONTCACHE instead of always_delete_dentry()
      debugfs: use DCACHE_DONTCACHE
      configfs: use DCACHE_DONTCACHE

Steven Rostedt (1):
      tracefs: Add d_delete to remove negative dentries

 Documentation/filesystems/porting.rst |  18 ++++
 fs/9p/vfs_dentry.c                    |   1 -
 fs/9p/vfs_super.c                     |  10 ++-
 fs/adfs/super.c                       |   2 +-
 fs/affs/super.c                       |   4 +-
 fs/afs/super.c                        |   4 +-
 fs/autofs/inode.c                     |   2 +-
 fs/btrfs/super.c                      |   2 +-
 fs/ceph/super.c                       |   2 +-
 fs/coda/inode.c                       |   2 +-
 fs/configfs/dir.c                     |   1 -
 fs/configfs/mount.c                   |   3 +-
 fs/dcache.c                           | 153 ++++++++++++++++++++--------------
 fs/debugfs/inode.c                    |   4 +-
 fs/devpts/inode.c                     |   2 +-
 fs/ecryptfs/main.c                    |   2 +-
 fs/efivarfs/super.c                   |   4 +-
 fs/exfat/super.c                      |   4 +-
 fs/fat/namei_msdos.c                  |   2 +-
 fs/fat/namei_vfat.c                   |   4 +-
 fs/fuse/dir.c                         |   7 --
 fs/fuse/fuse_i.h                      |   1 -
 fs/fuse/inode.c                       |   6 +-
 fs/gfs2/ops_fstype.c                  |   2 +-
 fs/hfs/super.c                        |   2 +-
 fs/hfsplus/super.c                    |   2 +-
 fs/hostfs/hostfs_kern.c               |   2 +-
 fs/hpfs/super.c                       |   2 +-
 fs/hugetlbfs/inode.c                  |   1 +
 fs/isofs/inode.c                      |   2 +-
 fs/jfs/super.c                        |   2 +-
 fs/kernfs/mount.c                     |   2 +-
 fs/libfs.c                            |  27 +++---
 fs/nfs/super.c                        |   2 +-
 fs/ntfs3/super.c                      |   3 +-
 fs/ocfs2/super.c                      |   2 +-
 fs/orangefs/super.c                   |   2 +-
 fs/overlayfs/super.c                  |   2 +-
 fs/proc/base.c                        |   9 +-
 fs/proc/generic.c                     |  10 ++-
 fs/proc/internal.h                    |   6 +-
 fs/proc/namespaces.c                  |   3 +-
 fs/proc/proc_sysctl.c                 |   7 +-
 fs/ramfs/inode.c                      |   1 +
 fs/smb/client/cifsfs.c                |   4 +-
 fs/tracefs/inode.c                    |  13 ++-
 fs/vboxsf/super.c                     |   2 +-
 include/linux/dcache.h                |   6 +-
 include/linux/fs.h                    |   4 +-
 include/linux/proc_fs.h               |   2 +
 ipc/mqueue.c                          |   1 +
 mm/shmem.c                            |   4 +-
 net/sunrpc/rpc_pipe.c                 |   2 +-
 53 files changed, 210 insertions(+), 159 deletions(-)