VFS : mount lock scalability for internal mounts

For a number of file systems that don't have a mount point (e.g. sockfs
and pipefs), they are not marked as long term. Therefore in
mntput_no_expire, all locks in vfs_mount lock are taken instead of just
local cpu's lock to aggregate reference counts when we release
reference to file objects.  In fact, only local lock need to have been
taken to update ref counts as these file systems are in no danger of
going away until we are ready to unregister them.

The attached patch marks file systems using kern_mount without
mount point as long term.  The contentions of vfs_mount lock
is now eliminated.  Before un-registering such file system,
kern_unmount should be called to remove the long term flag and
make the mount point ready to be freed.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
namespace: mnt_want_write: Remove unused label 'out'

I was studying the code and I saw that the out label is not being used
at all so I removed it and its usage from the function.

Signed-off-by: Kautuk Consul <consul.kautuk@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
switch create_mnt_ns() to saner calling conventions, fix double mntput() in nfs

Life is much saner if create_mnt_ns(mnt) drops mnt in case of error...
Switch it to such calling conventions, switch callers, fix double mntput() in
fs/nfs/super.c one.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
switch vfs_path_lookup() to struct path

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
nfs/super.c: local functions should be static

commit ae50c0b5 "pnfs: client stats" added additional information to
the output of /proc/self/mountstats. The new functions introduced are
only used in this file and should be marked static.

If CONFIG_NFS_V4_1 is not defined, empty stub functions are used.  If
CONFIG_NFS_V4 is not defined these stub functions are not used at all.
Adding static for the functions results in compile warnings:

fs/nfs/super.c:743: warning: 'show_sessions' defined but not used
fs/nfs/super.c:756: warning: 'show_pnfs' defined but not used

Fix this by adding a #ifdef CONFIG_NFS_V4 guard around the two
show_ functions.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
new helper: mount_subtree()

takes vfsmount and relative path, does lookup within that vfsmount
(possibly triggering automounts) and returns the result as root
of subtree suitable for return by ->mount() (i.e. a reference to
dentry and an active reference to its superblock grabbed, superblock
locked exclusive).

btrfs and nfs switched to it instead of open-coding the sucker.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
mount_subtree() pointless use-after-free

d'oh... we'd carefully pinned mnt->mnt_sb down, dropped mnt and attempt
to grab s_umount on mnt->mnt_sb.  The trouble is, *mnt might've been
overwritten by now...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: kill pointless helpers in namespace.c

mnt_{inc,dec}_count() is not cleaner than doing the corresponding
mnt_add_count() directly and mnt_set_count() is not used at all.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
unexport put_mnt_ns(), make create_mnt_ns() static outright

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: dentry_reset_mounted() doesn't use vfsmount argument

lose it

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: make do_kern_mount() static

the only user outside of fs/namespace.c has died

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: mnt_drop_write_file()

new helper (wrapper around mnt_drop_write()) to be used in pair with
mnt_want_write_file().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: start hiding vfsmount guts series

Almost all fields of struct vfsmount are used only by core VFS (and
a fairly small part of it, at that).  The plan: embed struct vfsmount
into struct mount, making the latter visible only to core parts of VFS.
Then move fields from vfsmount to mount, eventually leaving only
mnt_root/mnt_sb/mnt_flags in struct vfsmount.  Filesystem code still
gets pointers to struct vfsmount and remains unchanged; all such
pointers go to struct vfsmount embedded into the instances of struct
mount allocated by fs/namespace.c.  When fs/namespace.c et.al. get
a pointer to vfsmount, they turn it into pointer to mount (using
container_of) and work with that.

This is the first part of series; struct mount is introduced,
allocation switched to using it.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: spread struct mount - __lookup_mnt() result

switch __lookup_mnt() to returning struct mount *; callers adjusted.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: spread struct mount - namespace.c internal iterators

next_mnt() return value, first argument
skip_mnt_tree() return value and argument

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: spread struct mount - attach_mnt/detach_mnt

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: spread struct mount - commit_tree

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: spread struct mount - mount group id handling

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: spread struct mount - attach_recursive_mnt

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
vfs: spread struct mount - tree_contains_unbindable

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