IBM reported a soft lockup after applying the fix for the rename_lock
deadlock.  Commit c83ce989cb5f ("VFS: Fix the nfs sillyrename regression
in kernel 2.6.38") was found to be the culprit.

The nfs sillyrename fix used DCACHE_DISCONNECTED to indicate that the
dentry was killed.  This flag can be set on non-killed dentries too,
which results in infinite retries when trying to traverse the dentry
tree.

This patch introduces a separate flag: DCACHE_DENTRY_KILLED, which is
only set in d_kill() and makes try_to_ascend() test only this flag.

IBM reported successful test results with this patch.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Just the lookup flags.  Die, bastard, die...

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

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

This allows comparing hash and len in one operation on 64-bit
architectures.  Right now only __d_lookup_rcu() takes advantage of this,
since that is the case we care most about.

The use of anonymous struct/unions hides the alternate 64-bit approach
from most users, the exception being a few cases where we initialize a
'struct qstr' with a static initializer.  This makes the problematic
cases use a new QSTR_INIT() helper function for that (but initializing
just the name pointer with a "{ .name = xyzzy }" initializer remains
valid, as does just copying another qstr structure).

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

The calling conventions for __d_lookup_rcu() and dentry_cmp() are
annoying in different ways, and there is actually one single underlying
reason for both of the annoyances.

The fundamental reason is that we do the returned dentry sequence number
check inside __d_lookup_rcu() instead of doing it in the caller.  This
results in two annoyances:

 - __d_lookup_rcu() now not only needs to return the dentry and the
   sequence number that goes along with the lookup, it also needs to
   return the inode pointer that was validated by that sequence number
   check.

 - and because we did the sequence number check early (to validate the
   name pointer and length) we also couldn't just pass the dentry itself
   to dentry_cmp(), we had to pass the counted string that contained the
   name.

So that sequence number decision caused two separate ugly calling
conventions.

Both of these problems would be solved if we just did the sequence
number check in the caller instead.  There's only one caller, and that
caller already has to do the sequence number check for the parent
anyway, so just do that.

That allows us to stop returning the dentry->d_inode in that in-out
argument (pointer-to-pointer-to-inode), so we can make the inode
argument just a regular input inode pointer.  The caller can just load
the inode from dentry->d_inode, and then do the sequence number check
after that to make sure that it's synchronized with the name we looked
up.

And it allows us to just pass in the dentry to dentry_cmp(), which is
what all the callers really wanted.  Sure, dentry_cmp() has to be a bit
careful about the dentry (which is not stable during RCU lookup), but
that's actually very simple.

And now that dentry_cmp() can clearly see that the first string argument
is a dentry, we can use the direct word access for that, instead of the
careful unaligned zero-padding.  The dentry name is always properly
aligned, since it is a single path component that is either embedded
into the dentry itself, or was allocated with kmalloc() (see __d_alloc).

Finally, this also uninlines the nasty slow-case for dentry comparisons:
that one *does* need to do a sequence number check, since it will call
in to the low-level filesystems, and we want to give those a stable
inode pointer and path component length/start arguments.  Doing an extra
sequence check for that slow case is not a problem, though.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

all callers converted to d_make_root() by now

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

It's only used inside fs/dcache.c, and we're going to play games with it
for the word-at-a-time patches.  This time we really don't even want to
export it, because it really is an internal function to fs/dcache.c, and
has been since it was introduced.

Having it in that extremely hot header file (it's included in pretty
much everything, thanks to <linux/fs.h>) is a disaster for testing
different versions, and is utterly pointless.

We really should have some kind of header file diet thing, where we
figure out which parts of header files are really better off private and
only result in more expensive compiles.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

It did some odd things for unclear reasons.  As this is one of the
functions that gets changed when doing word-at-a-time compares, this is
yet another of the "don't change any semantics, but clean things up so
that subsequent patches don't get obscured by the cleanups".

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

.. and also use it in lookup_one_len() rather than open-coding it.

There aren't any performance-critical users, so inlining it is silly.
But it wouldn't matter if it wasn't for the fact that the word-at-a-time
dentry name patches want to conditionally replace the function, and
uninlining it sets the stage for that.

So again, this is a preparatory patch that doesn't change any semantics,
and only prepares for a much cleaner and testable word-at-a-time dentry
name accessor patch.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

These don't change any semantics, but they clean up the code a bit and
mark some arguments appropriately 'const'.

They came up as I was doing the word-at-a-time dcache name accessor
code, and cleaning this up now allows me to send out a smaller relevant
interesting patch for the experimental stuff.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>