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

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

This patch makes it possible to kill a process looping in
cont_expand_zero. A process may spend a lot of time in this function, so
it is desirable to be able to kill it.

It happened to me that I wanted to copy a piece data from the disk to a
file. By mistake, I used the "seek" parameter to dd instead of "skip". Due
to the "seek" parameter, dd attempted to extend the file and became stuck
doing so - the only possibility was to reset the machine or wait many
hours until the filesystem runs out of space and cont_expand_zero fails.
We need this patch to be able to terminate the process.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

For DAX, we want to be able to copy between iovecs and kernel addresses
that don't necessarily have a struct page.  This is a fairly simple
rearrangement for bvec iters to kmap the pages outside and pass them in,
but for user iovecs it gets more complicated because we might try various
different ways to kmap the memory.  Duplicating the existing logic works
out best in this case.

We need to be able to write zeroes to an iovec for reads from unwritten
ranges in a file.  This is performed by the new iov_iter_zero() function,
again patterned after the existing code that handles iovec iterators.

[AV: and export the buggers...]
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

total_objects could be 0 and is used as a denom.

While total_objects is a "long", total_objects == 0 unlikely happens for
3.12 and later kernels because 32-bit architectures would not be able to
hold (1 << 32) objects. However, total_objects == 0 may happen for kernels
between 3.1 and 3.11 because total_objects in prune_super() was an "int"
and (e.g.) x86_64 architecture might be able to hold (1 << 32) objects.
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: stable <stable@kernel.org> # 3.1+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Fixed coding style in dcache.c
Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

schedule_delayed_work() happening when the work is already pending is
a cheap no-op.  Don't bother with ->wbuf_queued logics - it's both
broken (cancelling ->wbuf_dwork leaves it set, as spotted by Jeff Harris)
and pointless.  It's cheaper to let schedule_delayed_work() handle that
case.
Reported-by: Jeff Harris <jefftharris@gmail.com>
Tested-by: Jeff Harris <jefftharris@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

The function which calls s_op->alloc_inode() is not inode_alloc(), but
instead alloc_inode() which lives in fs/inode.c .

The typo was there from the beginning from 5ea626aa (VFS: update
documentation, 2005) - there was no standalone inode_alloc() for the
whole kernel history.

Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Kirill Smelkov <kirr@nexedi.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

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

... rather than doing that in the guts of ->load_binary().
[updated to fix the bug spotted by Shentino - for SIGSEGV we really need
something stronger than send_sig_info(); again, better do that in one place]
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

the only in-tree instance checks d_unhashed() anyway,
out-of-tree code can preserve the current behaviour by
adding such check if they want it and we get an ability
to use it in cases where we *want* to be notified of
killing being inevitable before ->d_lock is dropped,
whether it's unhashed or not.  In particular, autofs
would benefit from that.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

The only reason for games with ->d_prune() was __d_drop(), which
was needed only to force dput() into killing the sucker off.

Note that lock_parent() can be called under ->i_lock and won't
drop it, so dentry is safe from somebody managing to kill it
under us - it won't happen while we are holding ->i_lock.

__dentry_kill() is called only with ->d_lockref.count being 0
(here and when picked from shrink list) or 1 (dput() and dropping
the ancestors in shrink_dentry_list()), so it will never be called
twice - the first thing it's doing is making ->d_lockref.count
negative and once that happens, nothing will increment it.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Now that d_invalidate always succeeds and flushes mount points use
it in stead of a combination of shrink_dcache_parent and d_drop
in proc_flush_task_mnt.  This removes the danger of a mount point
under /proc/<pid>/... becoming unreachable after the d_drop.
Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Now that d_invalidate always succeeds it is not longer necessary or
desirable to hard code d_drop calls into filesystem specific
d_revalidate implementations.

Remove the unnecessary d_drop calls and rely on d_invalidate
to drop the dentries.  Using d_invalidate ensures that paths
to mount points will not be dropped.
Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Now that d_invalidate can no longer fail, stop returning a useless
return code.  For the few callers that checked the return code update
remove the handling of d_invalidate failure.
Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Now that d_invalidate is the only caller of check_submounts_and_drop,
expand check_submounts_and_drop inline in d_invalidate.
Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Now that check_submounts_and_drop can not fail and is called from
d_invalidate there is no longer a need to call check_submounts_and_drom
from filesystem d_revalidate methods so remove it.
Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

With the introduction of mount namespaces and bind mounts it became
possible to access files and directories that on some paths are mount
points but are not mount points on other paths.  It is very confusing
when rm -rf somedir returns -EBUSY simply because somedir is mounted
somewhere else.  With the addition of user namespaces allowing
unprivileged mounts this condition has gone from annoying to allowing
a DOS attack on other users in the system.

The possibility for mischief is removed by updating the vfs to support
rename, unlink and rmdir on a dentry that is a mountpoint and by
lazily unmounting mountpoints on deleted dentries.

In particular this change allows rename, unlink and rmdir system calls
on a dentry without a mountpoint in the current mount namespace to
succeed, and it allows rename, unlink, and rmdir performed on a
distributed filesystem to update the vfs cache even if when there is a
mount in some namespace on the original dentry.

There are two common patterns of maintaining mounts: Mounts on trusted
paths with the parent directory of the mount point and all ancestory
directories up to / owned by root and modifiable only by root
(i.e. /media/xxx, /dev, /dev/pts, /proc, /sys, /sys/fs/cgroup/{cpu,
cpuacct, ...}, /usr, /usr/local).  Mounts on unprivileged directories
maintained by fusermount.

In the case of mounts in trusted directories owned by root and
modifiable only by root the current parent directory permissions are
sufficient to ensure a mount point on a trusted path is not removed
or renamed by anyone other than root, even if there is a context
where the there are no mount points to prevent this.

In the case of mounts in directories owned by less privileged users
races with users modifying the path of a mount point are already a
danger.  fusermount already uses a combination of chdir,
/proc/<pid>/fd/NNN, and UMOUNT_NOFOLLOW to prevent these races.  The
removable of global rename, unlink, and rmdir protection really adds
nothing new to consider only a widening of the attack window, and
fusermount is already safe against unprivileged users modifying the
directory simultaneously.

In principle for perfect userspace programs returning -EBUSY for
unlink, rmdir, and rename of dentires that have mounts in the local
namespace is actually unnecessary.  Unfortunately not all userspace
programs are perfect so retaining -EBUSY for unlink, rmdir and rename
of dentries that have mounts in the current mount namespace plays an
important role of maintaining consistency with historical behavior and
making imperfect userspace applications hard to exploit.

v2: Remove spurious old_dentry.
v3: Optimized shrink_submounts_and_drop
    Removed unsued afs label
v4: Simplified the changes to check_submounts_and_drop
    Do not rename check_submounts_and_drop shrink_submounts_and_drop
    Document what why we need atomicity in check_submounts_and_drop
    Rely on the parent inode mutex to make d_revalidate and d_invalidate
    an atomic unit.
v5: Refcount the mountpoint to detach in case of simultaneous
    renames.
Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

The new function detach_mounts comes in two pieces.  The first piece
is a static inline test of d_mounpoint that returns immediately
without taking any locks if d_mounpoint is not set.  In the common
case when mountpoints are absent this allows the vfs to continue
running with it's same cacheline foot print.

The second piece of detach_mounts __detach_mounts actually does the
work and it assumes that a mountpoint is present so it is slow and
takes namespace_sem for write, and then locks the mount hash (aka
mount_lock) after a struct mountpoint has been found.

With those two locks held each entry on the list of mounts on a
mountpoint is selected and lazily unmounted until all of the mount
have been lazily unmounted.

v7: Wrote a proper change description and removed the changelog
    documenting deleted wrong turns.
Signed-off-by: Eric W. Biederman <ebiederman@twitter.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

I am shortly going to add a new user of struct mountpoint that
needs to look up existing entries but does not want to create
a struct mountpoint if one does not exist.  Therefore to keep
the code simple and easy to read split out lookup_mountpoint
from new_mountpoint.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

To spot any possible problems call BUG if a mountpoint
is put when it's list of mounts is not empty.

AV: use hlist instead of list_head
Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Eric W. Biederman <ebiederman@twitter.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

In preparation for allowing mountpoints to be renamed and unlinked
in remote filesystems and in other mount namespaces test if on a dentry
there is a mount in the local mount namespace before allowing it to
be renamed or unlinked.

The primary motivation here are old versions of fusermount unmount
which is not safe if the a path can be renamed or unlinked while it is
verifying the mount is safe to unmount.  More recent versions are simpler
and safer by simply using UMOUNT_NOFOLLOW when unmounting a mount
in a directory owned by an arbitrary user.

Miklos Szeredi <miklos@szeredi.hu> reports this is approach is good
enough to remove concerns about new kernels mixed with old versions
of fusermount.

A secondary motivation for restrictions here is that it removing empty
directories that have non-empty mount points on them appears to
violate the rule that rmdir can not remove empty directories.  As
Linus Torvalds pointed out this is useful for programs (like git) that
test if a directory is empty with rmdir.

Therefore this patch arranges to enforce the existing mount point
semantics for local mount namespace.

v2: Rewrote the test to be a drop in replacement for d_mountpoint
v3: Use bool instead of int as the return type of is_local_mountpoint
Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

The current comments in d_invalidate about what and why it is doing
what it is doing are wildly off-base.  Which is not surprising as
the comments date back to last minute bug fix of the 2.2 kernel.

The big fat lie of a comment said: If it's a directory, we can't drop
it for fear of somebody re-populating it with children (even though
dropping it would make it unreachable from that root, we still might
repopulate it if it was a working directory or similar).

[AV] What we really need to avoid is multiple dentry aliases of the
same directory inode; on all filesystems that have ->d_revalidate()
we either declare all positive dentries always valid (and thus never
fed to d_invalidate()) or use d_materialise_unique() and/or d_splice_alias(),
which take care of alias prevention.

The current rules are:
- To prevent mount point leaks dentries that are mount points or that
  have childrent that are mount points may not be be unhashed.
- All dentries may be unhashed.
- Directories may be rehashed with d_materialise_unique

check_submounts_and_drop implements this already for well maintained
remote filesystems so implement the current rules in d_invalidate
by just calling check_submounts_and_drop.

The one difference between d_invalidate and check_submounts_and_drop
is that d_invalidate must respect it when a d_revalidate method has
earlier called d_drop so preserve the d_unhashed check in
d_invalidate.
Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

d_drop or check_submounts_and_drop called from d_revalidate can result
in renamed directories with child dentries being unhashed.  These
renamed and drop directory dentries can be rehashed after
d_materialise_unique uses d_find_alias to find them.
Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

On final mntput() we want fs shutdown to happen before return to
userland; however, the only case where we want it happen right
there (i.e. where task_work_add won't do) is MNT_INTERNAL victim.
Those have to be fully synchronous - failure halfway through module
init might count on having vfsmount killed right there.  Fortunately,
final mntput on MNT_INTERNAL vfsmounts happens on shallow stack.
So we handle those synchronously and do an analog of delayed fput
logics for everything else.

As the result, we are guaranteed that fs shutdown will always happen
on shallow stack.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Biederman's umount-on-rmdir series changes d_invalidate() to sumarily remove
mounts under the passed in dentry regardless of whether they are busy
or not. So calling this in fs/autofs4/expire.c:autofs4_tree_busy() is
definitely the wrong thing to do becuase it will silently umount entries
instead of just cleaning stale dentrys.

But this call shouldn't be needed and testing shows that automounting
continues to function without it.

As Al Viro correctly surmises the original intent of the call was to
perform what shrink_dcache_parent() does.

If at some time in the future I see stale dentries accumulating
following failed mounts I'll revisit the issue and possibly add a
shrink_dcache_parent() call if needed.
Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

* external dentry names get a small structure prepended to them
(struct external_name).
* it contains an atomic refcount, matching the number of struct dentry
instances that have ->d_name.name pointing to that external name.  The
first thing free_dentry() does is decrementing refcount of external name,
so the instances that are between the call of free_dentry() and
RCU-delayed actual freeing do not contribute.
* __d_move(x, y, false) makes the name of x equal to the name of y,
external or not.  If y has an external name, extra reference is grabbed
and put into x->d_name.name.  If x used to have an external name, the
reference to the old name is dropped and, should it reach zero, freeing
is scheduled via kfree_rcu().
* free_dentry() in dentry with external name decrements the refcount of
that name and, should it reach zero, does RCU-delayed call that will
free both the dentry and external name.  Otherwise it does what it
used to do, except that __d_free() doesn't even look at ->d_name.name;
it simply frees the dentry.

All non-RCU accesses to dentry external name are safe wrt freeing since they
all should happen before free_dentry() is called.  RCU accesses might run
into a dentry seen by free_dentry() or into an old name that got already
dropped by __d_move(); however, in both cases dentry must have been
alive and refer to that name at some point after we'd done rcu_read_lock(),
which means that any freeing must be still pending.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

AFAICS, prepend_name() is broken on SMP alpha.  Disclaimer: I don't have
SMP alpha boxen to reproduce it on.  However, it really looks like the race
is real.

CPU1: d_path() on /mnt/ramfs/<255-character>/foo
CPU2: mv /mnt/ramfs/<255-character> /mnt/ramfs/<63-character>

CPU2 does d_alloc(), which allocates an external name, stores the name there
including terminating NUL, does smp_wmb() and stores its address in
dentry->d_name.name.  It proceeds to d_add(dentry, NULL) and d_move()
old dentry over to that.  ->d_name.name value ends up in that dentry.

In the meanwhile, CPU1 gets to prepend_name() for that dentry.  It fetches
->d_name.name and ->d_name.len; the former ends up pointing to new name
(64-byte kmalloc'ed array), the latter - 255 (length of the old name).
Nothing to force the ordering there, and normally that would be OK, since we'd
run into the terminating NUL and stop.  Except that it's alpha, and we'd need
a data dependency barrier to guarantee that we see that store of NUL
__d_alloc() has done.  In a similar situation dentry_cmp() would survive; it
does explicit smp_read_barrier_depends() after fetching ->d_name.name.
prepend_name() doesn't and it risks walking past the end of kmalloc'ed object
and possibly oops due to taking a page fault in kernel mode.

Cc: stable@vger.kernel.org # 3.12+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Pull vfs fixes from Al Viro:
 "Assorted fixes + unifying __d_move() and __d_materialise_dentry() +
  minimal regression fix for d_path() of victims of overwriting rename()
  ported on top of that"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  vfs: Don't exchange "short" filenames unconditionally.
  fold swapping ->d_name.hash into switch_names()
  fold unlocking the children into dentry_unlock_parents_for_move()
  kill __d_materialise_dentry()
  __d_materialise_dentry(): flip the order of arguments
  __d_move(): fold manipulations with ->d_child/->d_subdirs
  don't open-code d_rehash() in d_materialise_unique()
  pull rehashing and unlocking the target dentry into __d_materialise_dentry()
  ufs: deal with nfsd/iget races
  fuse: honour max_read and max_write in direct_io mode
  shmem: fix nlink for rename overwrite directory

Pull cgroup fixes from Tejun Heo:
 "This is quite late but these need to be backported anyway.

  This is the fix for a long-standing cpuset bug which existed from
  2009.  cpuset makes use of PF_SPREAD_{PAGE|SLAB} flags to modify the
  task's memory allocation behavior according to the settings of the
  cpuset it belongs to; unfortunately, when those flags have to be
  changed, cpuset did so directly even whlie the target task is running,
  which is obviously racy as task->flags may be modified by the task
  itself at any time.  This obscure bug manifested as corrupt
  PF_USED_MATH flag leading to a weird crash.

  The bug is fixed by moving the flag to task->atomic_flags.  The first
  two are prepatory ones to help defining atomic_flags accessors and the
  third one is the actual fix"

* 'for-3.17-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cpuset: PF_SPREAD_PAGE and PF_SPREAD_SLAB should be atomic flags
  sched: add macros to define bitops for task atomic flags
  sched: fix confusing PFA_NO_NEW_PRIVS constant

Pull ARM SoC fixes from Olof Johansson:
 "Here's our last set of fixes for 3.17.  Most of these are for TI
  platforms, fixing some noisy Kconfig issues, runtime clock and power
  issues on several platforms and NAND timings on DRA7.

  There are also a couple of bug fixes for i.MX, one for QCOM and a
 small fix to avoid section mismatch noise on PXA.

  Diffstat looks large, partially due to some tables being updated and
  thus touching many lines.  The qcom gsbi change also restructures
  clock management a bit and thus touches a bunch of lines.

  All in all, a bit more changes than we'd like at this point, but
  nothing stands out as risky either so it seems like the right thing to
  send it up now instead of holding it to the merge window"

* tag 'fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc:
  drivers/soc: qcom: do not disable the iface clock in probe
  ARM: imx: fix .is_enabled() of shared gate clock
  ARM: OMAP3: Fix I/O chain clock line assertion timed out error
  ARM: keystone: dts: fix bindings for pcie and usb clock nodes
  bus: omap_l3_noc: Fix connID for OMAP4
  ARM: DT: imx53: fix lvds channel 1 port
  ARM: dts: cm-t54: fix serial console power supply.
  ARM: dts: dra7-evm: Fix NAND GPMC timings
  ARM: pxa: fix section mismatch warning for pxa_timer_nodt_init
  ARM: OMAP: Fix Kconfig warning for omap1

Pull MIPS fixes from Ralf Baechle:
 "The final round of fixes.  One corner case in the math emulator and
  another one in the mcount function for ftrace"

* 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus:
  MIPS: mcount: Adjust stack pointer for static trace in MIPS32
  MIPS: Fix MFC1 & MFHC1 emulation for 64-bit MIPS systems

Pull x86 fixes from Ingo Molnar:
 "This has:

   - EFI revert to fix a boot regression
   - early_ioremap() fix for boot failure
   - KASLR fix for possible boot failures
   - EFI fix for corrupted string printing
   - remove a misleading EFI bootup 'failed!' error message

  Unfortunately it's all rather close to the merge window"

* 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/efi: Truncate 64-bit values when calling 32-bit OutputString()
  x86/efi: Delete misleading efi_printk() error message
  Revert "efi/x86: efistub: Move shared dependencies to <asm/efi.h>"
  x86/kaslr: Avoid the setup_data area when picking location
  x86 early_ioremap: Increase FIX_BTMAPS_SLOTS to 8

Only exchange source and destination filenames
if flags contain RENAME_EXCHANGE.
In case if executable file was running and replaced by
other file /proc/PID/exe should still show correct file name,
not the old name of the file by which it was replaced.

The scenario when this bug manifests itself was like this:
* ALT Linux uses rpm and start-stop-daemon;
* during a package upgrade rpm creates a temporary file
  for an executable to rename it upon successful unpacking;
* start-stop-daemon is run subsequently and it obtains
  the (nonexistant) temporary filename via /proc/PID/exe
  thus failing to identify the running process.

Note that "long" filenames (> DNAiME_INLINE_LEN) are still
exchanged without RENAME_EXCHANGE and this behaviour exists
long enough (should be fixed too apparently).
So this patch is just an interim workaround that restores
behavior for "short" names as it was before changes
introduced by commit da1ce067 ("vfs: add cross-rename").

See https://lkml.org/lkml/2014/9/7/6 for details.

AV: the comments about being more careful with ->d_name.hash
than with ->d_name.name are from back in 2.3.40s; they
became obsolete by 2.3.60s, when we started to unhash the
target instead of swapping hash chain positions followed
by d_delete() as we used to do when dcache was first
introduced.
Acked-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Cc: stable@vger.kernel.org
Fixes: da1ce067 "vfs: add cross-rename"
Signed-off-by: Mikhail Efremov <sem@altlinux.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

and do it along with ->d_name.len there
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... renaming it into dentry_unlock_for_move() and making it more
symmetric with dentry_lock_for_move().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

it folds into __d_move() now
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... thus making it much closer to (now unreachable, BTW) IS_ROOT(dentry)
case in __d_move().  A bit more and it'll fold in.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

list_del() + list_add() is a slightly pessimised list_move()
list_del() + INIT_LIST_HEAD() is a slightly pessimised list_del_init()

Interleaving those makes the resulting code even worse.  And harder to follow...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... and get rid of duplicate BUG_ON() there
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>