lockd: protect nlm_blocked access in nlmsvc_retry_blocked

In nlmsvc_retry_blocked, the check that the list is non-empty and acquiring
the pointer of the first entry is unprotected by any lock.  This allows a rare
race condition when there is only one entry on the list.  A function such as
nlmsvc_grant_callback() can be called, which will temporarily remove the entry
from the list.  Between the list_empty() and list_entry(),the list may become
empty, causing an invalid pointer to be used as an nlm_block, leading to a
possible crash.

This patch adds the nlm_block_lock around these calls to prevent concurrent
use of the nlm_blocked list.

This was a regression introduced by
f904be9cc77f361d37d71468b13ff3d1a1823dea  "lockd: Mostly remove BKL from
the server".

Cc: Bryan Schumaker <bjschuma@netapp.com>
Cc: stable@vger.kernel.org
Signed-off-by: David Jeffery <djeffery@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
nfsd4: fix minorversion support interface

You can turn on or off support for minorversions using e.g.

	echo "-4.2" >/proc/fs/nfsd/versions

However, the current implementation is a little wonky.  For example, the
above will turn off 4.2 support, but it will also turn *on* 4.1 support.

This didn't matter as long as we only had 2 minorversions, which was
true till very recently.

And do a little cleanup here.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
svcrdma: underflow issue in decode_write_list()

My static checker marks everything from ntohl() as untrusted and it
complains we could have an underflow problem doing:

	return (u32 *)&ary->wc_array[nchunks];

Also on 32 bit systems the upper bound check could overflow.

Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
linked-list: Remove __list_for_each

__list_for_each used to be the non prefetch() aware list walking
primitive.  When we removed the prefetch macros from the list routines,
it became redundant.  Given it does exactly the same thing as
list_for_each now, we might as well remove it and call list_for_each
directly.

All users of __list_for_each have been converted to list_for_each calls
in the current merge window.

Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Merge branch 'for-3.11' of git://linux-nfs.org/~bfields/linux

Pull nfsd bugfixes from Bruce Fields:
 "Just three minor bugfixes"

* 'for-3.11' of git://linux-nfs.org/~bfields/linux:
  svcrdma: underflow issue in decode_write_list()
  nfsd4: fix minorversion support interface
  lockd: protect nlm_blocked access in nlmsvc_retry_blocked