acct: new lifetime rules

Do not reuse bsd_acct_struct after closing the damn thing.
Structure lifetime is controlled by refcount now.  We also
have a mutex in there, held over closing and writing (the
file is O_APPEND, so we are not losing any concurrency).

As the result, we do not need to bother with get_file()/fput()
on log write anymore.  Moreover, do_acct_process() only needs
acct itself; file and pidns are picked from it.

Killed instances are distinguished by having NULL ->ns.
Refcount is protected by acct_lock; anybody taking the
mutex needs to grab a reference first.

The things will get a lot simpler in the next commits - this
is just the minimal chunk switching to the new lifetime rules.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
acct: simplify check_free_space()

a) file can't be NULL
b) file can't be changed under us
c) all writes are serialized by acct->lock; no need to mess with
spinlock there.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
acct: get rid of acct_list

Put these suckers on per-vfsmount and per-superblock lists instead.
Note: right now it's still acct_lock for everything, but that's
going to change.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
acct: get rid of acct_lock for acct->count

* make acct->count atomic and acct freeing - rcu-delayed.
* instead of grabbing acct_lock around the places where we take a reference,
do that under rcu_read_lock() with atomic_long_inc_not_zero().
* have the new acct locked before making ns->bacct point to it

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
drop ->s_umount around acct_auto_close()

just repeat the frozen check after regaining it, and check that sb
is still alive.  If several threads hit acct_auto_close() at the
same time, acct_auto_close() will survive that just fine.  And we
really don't want to play with writes and closing the file with
->s_umount held exclusive - it's a deadlock country.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
make acct_kill() wait for file closing.

Do actual closing of file via schedule_work().  And use
__fput_sync() there.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
acct: move mnt_pin() upwards.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
start carving bsd_acct_struct up

pull generic parts into struct fs_pin.  Eventually we want those
to replace mnt_pin()/mnt_unpin() mess; that stuff will move to
fs/*.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
take fs_pin stuff to fs/*

Add a new field to fs_pin - kill(pin).  That's what umount and r/o remount
will be calling for all pins attached to vfsmount and superblock resp.
Called after bumping the refcount, so it won't go away under us.  Dropping
the refcount is responsibility of the instance.  All generic stuff moved to
fs/fs_pin.c; the next step will rip all the knowledge of kernel/acct.c from
fs/super.c and fs/namespace.c.  After that - death to mnt_pin(); it was
intended to be usable as generic mechanism for code that wants to attach
objects to vfsmount, so that they would not make the sucker busy and
would get killed on umount.  Never got it right; it remained acct.c-specific
all along.  Now it's very close to being killable.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
make fs/{namespace,super}.c forget about acct.h

These externs belong in fs/internal.h.  Rename (they are not acct-specific
anymore) and move them over there.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
death to mnt_pinned

Rather than playing silly buggers with vfsmount refcounts, just have
acct_on() ask fs/namespace.c for internal clone of file->f_path.mnt
and replace it with said clone.  Then attach the pin to original
vfsmount.  Voila - the clone will be alive until the file gets closed,
making sure that underlying superblock remains active, etc., and
we can drop the original vfsmount, so that it's not kept busy.
If the file lives until the final mntput of the original vfsmount,
we'll notice that there's an fs_pin (one in bsd_acct_struct that
holds that file) and mnt_pin_kill() will take it out.  Since
->kill() is synchronous, we won't proceed past that point until
these files are closed (and private clones of our vfsmount are
gone), so we get the same ordering warranties we used to get.

mnt_pin()/mnt_unpin()/->mnt_pinned is gone now, and good riddance -
it never became usable outside of kernel/acct.c (and racy wrt
umount even there).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
kernel/acct.c: fix coding style warnings and errors

Signed-off-by: Ionut Alexa <ionut.m.alexa@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
fs: call rename2 if exists

Christoph Hellwig suggests:

1) make vfs_rename call ->rename2 if it exists instead of ->rename
2) switch all filesystems that you're adding NOREPLACE support for to
   use ->rename2
3) see how many ->rename instances we'll have left after a few
   iterations of 2.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
bad_inode: add ->rename2()

so we return -EIO instead of -EINVAL.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
btrfs: add RENAME_NOREPLACE

RENAME_NOREPLACE is trivial to implement for most filesystems: switch over
to ->rename2() and check for the supported flags.  The rest is done by the
VFS.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Chris Mason <clm@fb.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
shmem: support RENAME_NOREPLACE

Implement ->rename2 instead of ->rename.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
shmem: support RENAME_EXCHANGE

This is really simple in tmpfs since the VFS already takes care of
shuffling the dentries.  Just adjust nlink on parent directories and touch
c & mtimes.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
hostfs: support rename flags

Support RENAME_NOREPLACE and RENAME_EXCHANGE flags on hostfs if the
underlying filesystem supports it.

Since renameat2(2) is not yet in any libc, use syscall(2) to invoke the
renameat2 syscall.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Richard Weinberger <richard@nod.at>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
cifs: support RENAME_NOREPLACE

This flag gives CIFS the ability to support its native rename semantics.

Implementation is simple: just bail out before trying to hack around the
noreplace semantics.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Steve French <smfrench@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
VFS: allow ->d_manage() to declare -EISDIR in rcu_walk mode.

In REF-walk mode, ->d_manage can return -EISDIR to indicate
that the dentry is not really a mount trap (or even a mount point)
and that any mounts or any DCACHE_NEED_AUTOMOUNT flag should be
ignored.

RCU-walk mode doesn't currently support this, so if there is a dentry
with DCACHE_NEED_AUTOMOUNT set but which shouldn't be a mount-trap,
lookup_fast() will always drop in REF-walk mode.

With this patch, an -EISDIR from ->d_manage will always cause mounts
and automounts to be ignored, both in REF-walk and RCU-walk.

Bug-fixed-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Ian Kent <raven@themaw.net>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>