Commit Graph

282 Commits

Author SHA1 Message Date
Kirk McKusick
43a993bb7d For performance reasons, it is useful to have a single string used as
the name of a filesystem when setting it as the first parameter to the
getnewvnode() function. Most filesystems call getnewvnode from just one
place so can use a literal string as the first parameter. However, NFS
calls getnewvnode from two places, so we create a global constant string
that can be used by the two instances. This change also collapses two
instances of getnewvnode() in the UFS filesystem to a single call.

Reviewed by: kib
Tested by:   Peter Holm
2015-11-29 21:01:02 +00:00
Rick Macklem
b179878dde Revert r283330 since it broke directory caching in the client.
At this time I cannot see a way to fix directory caching when it
has partial blocks in the buffer cache, due to the fact that the
syscall's uio_offset won't stay the same as the lblkno * NFS_DIRBLKSIZ
offset.

Reported by:	bde
MFC after:	2 weeks
2015-11-21 00:15:41 +00:00
Rick Macklem
f315383406 mnt_stat.f_iosize (which is used to set bo_bsize) must be set to
the largest size of buffer cache block or the mapping of the buffer
is bogus. When a mount with rsize=4096,wsize=4096 was done, f_iosize
would be set to 4096. This resulted in corrupted directory data, since
the buffer cache block size for directories is NFS_DIRBLKSIZ (8192).
This patch fixes the code so that it always sets f_iosize to at least
NFS_DIRBLKSIZ.

Tested by:	krichy@cflinux.hu
PR:		177971
MFC after:	2 weeks
2015-11-17 01:44:26 +00:00
Conrad Meyer
b5af3f30a7 nfsclient: Protest loudly when GETATTR responses are invalid
BROKEN NFS SERVER OR MIDDLEWARE: Certain WAN "accelerators" attempt to cache
NFS GETATTR traffic, but actually corrupt it (e.g., responding to requests
with attributes for totally different files).

Warn very verbosely when this is detected. Linux' NFS client has a similar
warning.

Adds a sysctl/tunable (vfs.nfs.fileid_maxwarnings) to configure the quantity
of warnings; default to 10. (Zero disables; -1 is unlimited.)

Adds a failpoint to aid in validating the warning / behavior with a
non-broken server. Use something like:

    sysctl 'debug.fail_point.nfscl_force_fileid_warning=10%return(1)'

Reviewed by:	rmacklem
Approved by:	markj (mentor)
Sponsored by:	EMC / Isilon Storage Division
Differential Revision:	https://reviews.freebsd.org/D3304
2015-08-05 22:27:30 +00:00
Rick Macklem
2a3508eb48 If a "principal" argument isn't provided for a Kerberized NFS mount,
the kernel would generate a bogus one with a ":/<path>" suffix.
This would only occur for the case where there was no explicit
"principal" argument and the getaddrinfo() call in mount_nfs.c failed to a
return a cannonical name for the server.
This patch fixes this unusual case.

PR:		201073
Submitted by:	masato@itc.naist.jp
MFC after:	2 weeks
2015-07-03 22:11:07 +00:00
Rick Macklem
d189dcb6e2 Alex Burlyga reported a POLA violation for the new NFS client as
compared to the old NFS client via email to the freebsd-fs@ mailing list.
For the new client, when multiple clients attempted to create a symbolic
link concurrently, more that one client would report success instead of
EEXIST. This was caused by code in the new client that mapped EEXIST to
OK assuming it was caused by a retried RPC request.
Since the old client did not do this, the patch defaults to the old
behaviour and permits the new behaviour to be enabled via a sysctl.

Reported by:	alex.burlyga.ietf@gmail.com
Tested by:	alex.burlyga.ietf@gmail.com
MFC after:	2 weeks
2015-07-03 01:15:21 +00:00
Gleb Smirnoff
093ebe1d28 o Un-inline vm_pager_get_pages(), vm_pager_get_pages_async().
o Provide an extensive set of assertions for input array of pages.
o Remove now duplicate assertions from different pagers.

Sponsored by:	Nginx, Inc.
Sponsored by:	Netflix
2015-06-17 22:44:27 +00:00
Rick Macklem
262a84286d The NFS client generated directory block(s) with d_fileno == 0
so that it would not return less data than requested.
Since returning less directory data than requested is not a problem
for FreeBSD and even UFS no longer returns directory structures
with d_fileno == 0, this patch stops the client from doing this.
Although entries with d_fileno == 0 should not be a problem,
the man pages no longer document that these entries should be
ignored, so there was a concern that these entries might be an
issue in the future.

Suggested by:	trasz
Tested by:	trasz
MFC after:	2 weeks
2015-05-23 21:58:41 +00:00
Rick Macklem
86b9457f5b The NFS client wasn't handling getdirentries(2) requests for sizes
that are not an exact multiple of DIRBLKSIZ correctly. Fortunately
readdir(3) always uses an exact multiple of DIRBLKSIZ, so few applications
were affected. This patch fixes this problem by reducing the size
of the directory read to an exact multiple of DIRBLKSIZ.

Tested by:	trasz
Reported by:	trasz
Reviewed by:	trasz
MFC after:	2 weeks
2015-05-21 23:14:18 +00:00
Alexander Motin
a87627b26b Do not promote large async writes to sync.
Present implementation of large sync writes is too strict and so can be
quite slow.  Instead of doing that, execute large async write in chunks,
syncing each chunk separately.

It would be good to fix large sync writes too, but I leave it to somebody
with more skills in this area.

Reviewed by:	rmacklem
MFC after:	1 week
2015-05-14 10:04:42 +00:00
Rick Macklem
7cfdc2a7bc MAXBSIZE defines both the largest UFS block size and the
largest size for a buffer in the buffer cache. This patch
defines a new constant MAXBCACHEBUF, which is the largest
size for a buffer in the buffer cache. Having a separate
constant allows MAXBCACHEBUF to be set larger than MAXBSIZE
on a per-architecture basis, so that NFS can do larger read/writes
for these architectures. It modifies sys/param.h so that BKVASIZE
can also be set on a per-architecture basis.
A couple of cases where NFS used MAXBSIZE instead of NFS_MAXBSIZE
is fixed as well.

Differential Revision:	https://reviews.freebsd.org/D2330
Reviewed by:	mav, kib
MFC after:	2 weeks
2015-04-25 00:52:01 +00:00
Pedro F. Giffuni
2f39c91019 Prevent a double free.
This is similar to r281756 so set the ptr NULL after free as a safety belt
against future changes.

Obtained from:	HardenedBSD (b2e77ced9ae213d358b44d98f552d9ae4636ecac)
Submitted by:	Oliver Pinter
Revewed by:	rmacklem
2015-04-20 16:40:13 +00:00
Pedro F. Giffuni
a3a4b110da nfsrpc_createv4: fix double free.
Reported by:	Oliver Pinter, clang static checker
Obtained from:	HardenedBSD (commit 63cac77c42c0c3fc67da62f97d5ab651d52ae707)
Reviewed by:	rmacklem
MFC after:	5 days
2015-04-19 23:55:59 +00:00
Alexander Motin
afdfc9a40d Change wcommitsize default from one empirical value to another.
The new value is more predictable with growing RAM size:

        hibufspace maxvnodes      old      new
i386:
  256MB   32980992     15800  2198732  2097152
    2GB   94027776    107677   878764  4194304
amd64:
  256MB   32980992     15800  2198732  2097152
    1GB  114114560     68062  1678155  4194304
    4GB  217055232    111807  1955452  4194304
   16GB 1717846016    337308  5097465 16777216
   64GB 1734918144   1164427  1490479 16777216
  256GB 1734918144   4426453   391983 16777216

Reviewed by:	rmacklem
MFC after:	2 weeks
2015-04-19 11:34:41 +00:00
Edward Tomasz Napierala
50a220c699 Replace "new NFS" with just "NFS" in some sysctl description strings.
Sponsored by:	The FreeBSD Foundation
2015-04-19 06:18:41 +00:00
Rick Macklem
dda11d4ab9 File systems that do not use the buffer cache (such as ZFS) must
use VOP_FSYNC() to perform the NFS server's Commit operation.
This patch adds a mnt_kern_flag called MNTK_USES_BCACHE which
is set by file systems that use the buffer cache. If this flag
is not set, the NFS server always does a VOP_FSYNC().
This should be ok for old file system modules that do not set
MNTK_USES_BCACHE, since calling VOP_FSYNC() is correct, although
it might not be optimal for file systems that use the buffer cache.

Reviewed by:	kib
MFC after:	2 weeks
2015-04-15 20:16:31 +00:00
Gleb Smirnoff
4d6481a4c9 o Enhance vm_pager_free_nonreq() function:
- Allow to call the function with vm object lock held.
  - Allow to specify reqpage that doesn't match any page in the region,
    meaning freeing all pages.
o Utilize the new function in couple more places in vnode pager.

Reviewed by:	alc, kib
Sponsored by:	Netflix
Sponsored by:	Nginx, Inc.
2015-03-17 19:19:19 +00:00
Rick Macklem
07d491dede r245508 modified the NFS client's Setattr RPC to
use VA_UTIMES_NULL to indicate whether it should
set the time to the current tod on the server.
This had the side effect of making the NFS client
use the client's timestamp for exclusive create,
starting with FreeBSD9.2.
Unfortunately a bug in some Solaris NFS servers
causes these servers to return NFS_OK to the
Setattr RPC done during exclusive create, but not
actually set the file's mode, leaving the file's
mode == 0.
This patch restores the NFS client's behaviour to
use the server's tod for the exclusive open's
Setattr RPC, to avoid the Solaris server bug and
to restore the pre-FreeBSD9.2 NFS behaviour.

Discussed on:	freebsd-fs
PR:	186293
MFC after:	3 months
2014-12-28 21:13:52 +00:00
Rick Macklem
2f88b3d20a Delete some duplicate code that was harmless because
exactly the same code is at the end of the nfscl_checksattr()
function that is called just before it. As such, this code
had already been executed and didn't do anything.

MFC after:	1 week
2014-12-25 22:29:37 +00:00
Rick Macklem
62c23db947 Fix kernel builds with "options NFS_DEBUG" that
were broken by r276096. Also delete the two
kernel options NFS_GATHERDELAY, NFS_WDELAYHASHSIZ
which are no longer used.

Reported by:	bz
2014-12-23 14:24:36 +00:00
Rick Macklem
c15882f091 Remove the old NFS client and server from head,
which means that the NFSCLIENT and NFSSERVER
kernel options will no longer work. This commit
only removes the kernel components. Removal of
unused code in the user utilities will be done
later. This commit does not include an addition
to UPDATING, but that will be committed in a
few minutes.

Discussed on: freebsd-fs
2014-12-23 00:47:46 +00:00
Konstantin Belousov
6c21f6edb8 The VOP_LOOKUP() implementations for CREATE op do not put the name
into namecache, to avoid cache trashing when doing large operations.
E.g., tar archive extraction is not usually followed by access to many
of the files created.

Right now, each VOP_LOOKUP() implementation explicitely knowns about
this quirk and tests for both MAKEENTRY flag presence and op != CREATE
to make the call to cache_enter().  Centralize the handling of the
quirk into VFS, by deciding to cache only by MAKEENTRY flag in VOP.
VFS now sets NOCACHE flag for CREATE namei() calls.

Note that the change in semantic is backward-compatible and could be
merged to the stable branch, and is compatible with non-changed
third-party filesystems which correctly handle MAKEENTRY.

Suggested by:	Chris Torek <torek@pi-coral.com>
Reviewed by:	mckusick
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
2014-12-18 10:01:12 +00:00
Edward Tomasz Napierala
2fbe0cff73 Fix handling of "conn" mount_nfs(8) option.
Reviewed by:	rmacklem@
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
2014-10-30 09:25:03 +00:00
Edward Tomasz Napierala
5a06ac3540 Add support for "timeo", "actimeo", "noac", and "proto" options
to mount_nfs(8).  They are implemented on Linux, OS X, and Solaris,
and thus can be expected to appear in automounter maps.

Reviewed by:	rmacklem@
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
2014-10-30 08:50:01 +00:00
Rick Macklem
6a30c96cdc Clip the settings for the NFS rsize, wsize mount options
to a power of 2. For non-power of 2 settings, intermittent
page faults have been reported. Although the bug that causes
these page faults/crashes has not been identified, it does
not appear to occur when rsize, wsize is a power of 2.

Reported by:	tcberner@gmail.com
MFC after:	2 weeks
2014-10-22 22:27:51 +00:00
Rick Macklem
fcf121d481 Revert r273481 so it can be recoded using fls(), which
some feel will make it more readable.
2014-10-22 21:57:35 +00:00
Rick Macklem
88cc4e92da Clip the settings for the NFS rsize, wsize mount options
to a power of 2. For non-power of 2 settings, intermittent
page faults have been reported. Although the bug that causes
these page faults/crashes has not been identified, it does
not appear to occur when rsize, wsize is a power of 2.

Reported by:	tcberner@gmail.com
MFC after:	2 weeks
2014-10-22 20:47:11 +00:00
Davide Italiano
2be111bf7d Follow up to r225617. In order to maximize the re-usability of kernel code
in userland rename in-kernel getenv()/setenv() to kern_setenv()/kern_getenv().
This fixes a namespace collision with libc symbols.

Submitted by:   kmacy
Tested by:      make universe
2014-10-16 18:04:43 +00:00
Alan Cox
396b3e34b4 Avoid an exclusive acquisition of the object lock on the expected execution
path through the NFS clients' getpages functions.

Introduce vm_pager_free_nonreq().  This function can be used to eliminate
code that is duplicated in many getpages functions.  Also, in contrast to
the code that currently appears in those getpages functions,
vm_pager_free_nonreq() avoids acquiring an exclusive object lock in one
case.

Reviewed by:	kib
MFC after:	6 weeks
Sponsored by:	EMC / Isilon Storage Division
2014-09-14 18:07:55 +00:00
Konstantin Belousov
65589a29f4 Check for the cross-device cross-link attempt in the VFS, instead of
forcing filesystem VOP_LINK() methods to repeat the code.  In
tmpfs_link(), remove redundand check for the type of the source,
already done by VFS.

Note that NFS server already performs this check before calling
VOP_LINK().

Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
2014-07-16 14:04:46 +00:00
Rick Macklem
c59e4cc34d Merge the NFSv4.1 server code in projects/nfsv4.1-server over
into head. The code is not believed to have any effect
on the semantics of non-NFSv4.1 server behaviour.
It is a rather large merge, but I am hoping that there will
not be any regressions for the NFS server.

MFC after:	1 month
2014-07-01 20:47:16 +00:00
Rick Macklem
2d5f835917 There might be a potential race condition for the NFSv4 client
when a newly created file has another open done on it that
update the open mode. This patch moves the code that updates
the open mode up into the block where the mutex is held to
ensure this cannot happen. No bug caused by this potential
race has been observed, but this fix is a safety belt to ensure
it cannot happen.

MFC after:	2 weeks
2014-06-28 21:47:15 +00:00
Rick Macklem
c0990edac6 Modify the NFSv4 client's Pathconf RPC (actually a Getattr Op.)
so that it only does the RPC for names that are answered by the RPC.
Doing the RPC for other names is harmless, but unnecessary.

MFC after:	2 weeks
2014-04-23 22:13:10 +00:00
Rick Macklem
9eeef7464b Fixes mkdir for the NFSv2 client that was broken by r264705.
Reported by:	bdrewery
MFC after:	2 weeks
2014-04-22 04:42:46 +00:00
Rick Macklem
c7b560b9b4 For an NFSv4 mount with the "nocto" option, don't get the
up to date file attributes upon close. This reduces the
Getattr RPC count by about 65% for software builds.

MFC after:	2 weeks
2014-04-21 19:10:23 +00:00
Rick Macklem
c3e4a7261c Modify the NFSv4 client create/mkdir RPC so that it acquires
post-create/mkdir directory attributes. This allows the RPC to
name cache the newly created directory and reduces the lookup RPC
count for applications creating a lot of directories.

MFC after:	2 weeks
2014-04-20 22:19:00 +00:00
Rick Macklem
de1a42bd0c Modify the NFSv4 client open/create RPC so that it acquires
post-open/create directory attributes. This allows the RPC to
name cache the newly created file and reduces the lookup RPC
count by about 10% for software builds.

MFC after:	2 weeks
2014-04-19 19:40:20 +00:00
Rick Macklem
a6f8e64e74 Modify the Lookup RPC for NFSv4 so that it acquires directory
attributes. This allows the client to cache directory names
when they are looked up, reducing the Lookup RPC count by
about 40% for software builds.

MFC after:	2 weeks
2014-04-18 22:05:34 +00:00
Robert Watson
4a14441044 Update kernel inclusions of capability.h to use capsicum.h instead; some
further refinement is required as some device drivers intended to be
portable over FreeBSD versions rely on __FreeBSD_version to decide whether
to include capability.h.

MFC after:	3 weeks
2014-03-16 10:55:57 +00:00
Rick Macklem
b921158ae0 The NFSv4 client was passing both the p and cred arguments to
nfsv4_fillattr() as NULLs for the Getattr callback. This caused
nfsv4_fillattr() to not fill in the Change attribute for the reply.
I believe this was a violation of the RFC, but had little effect on
server behaviour. This patch passes a non-NULL p argument to fix this.

MFC after:	1 week
2013-12-24 00:48:39 +00:00
Rick Macklem
6b8fe5d59d The NFSv4.1 client didn't return NFSv4.1 specific error codes
for the Getattr and Recall callbacks. This patch fixes it.
Since the NFSv4.1 specific error codes would only happen for
abnormal circumstances, this patch has little effect, in practice.

MFC after:	1 week
2013-12-23 15:16:53 +00:00
Rick Macklem
cf766161ff For software builds, the NFS client does many small
synchronous (with FILE_SYNC) writes because non-contiguous
byte ranges in the same buffer cache block are being
written. This patch adds a new mount option "noncontigwr"
which allows the non-contiguous byte ranges to be combined,
with the dirty byte range becoming the superset of the bytes
that are dirty, if the file has not been file locked.
This reduces the number of writes significantly for software
builds. The only case where this change might break existing
applications is where an application is writing
non-overlapping byte ranges within the same buffer cache block
of a file from multiple clients concurrently.
Since such an application would normally do file locking on
the file, avoiding the byte range merge for files that have
been file locked should be sufficient for most (maybe all?) cases.

Submitted by:	jhb (earlier version)
Reviewed by:	kib
MFC after:	3 weeks
2013-12-07 23:05:59 +00:00
Sergey Kandaurov
0d8dc7cc39 - Nuke a second copy of nfscl_attrcache extern declarations from under
ifdef KDTRACE_HOOKS.  This fixes kernel build with options KDTRACE_HOOKS.
- Fix style inconsistencies.
2013-11-26 22:41:40 +00:00
Gleb Smirnoff
285e7a2d97 Fix build, attempt two. 2013-11-26 20:27:57 +00:00
Gleb Smirnoff
6882b8ea66 Fix build. 2013-11-26 10:34:34 +00:00
Attilio Rao
54366c0bd7 - For kernel compiled only with KDTRACE_HOOKS and not any lock debugging
option, unbreak the lock tracing release semantic by embedding
  calls to LOCKSTAT_PROFILE_RELEASE_LOCK() direclty in the inlined
  version of the releasing functions for mutex, rwlock and sxlock.
  Failing to do so skips the lockstat_probe_func invokation for
  unlocking.
- As part of the LOCKSTAT support is inlined in mutex operation, for
  kernel compiled without lock debugging options, potentially every
  consumer must be compiled including opt_kdtrace.h.
  Fix this by moving KDTRACE_HOOKS into opt_global.h and remove the
  dependency by opt_kdtrace.h for all files, as now only KDTRACE_FRAMES
  is linked there and it is only used as a compile-time stub [0].

[0] immediately shows some new bug as DTRACE-derived support for debug
in sfxge is broken and it was never really tested.  As it was not
including correctly opt_kdtrace.h before it was never enabled so it
was kept broken for a while.  Fix this by using a protection stub,
leaving sfxge driver authors the responsibility for fixing it
appropriately [1].

Sponsored by:	EMC / Isilon storage division
Discussed with:	rstone
[0] Reported by:	rstone
[1] Discussed with:	philip
2013-11-25 07:38:45 +00:00
Rick Macklem
42b6336a98 Fix an NFSv4.1 client specific case where a forced dismount would hang.
The hang occurred in nfsv4_setsequence() when it couldn't find an
available session slot and is fixed by checking for a forced dismount
in progress and just returning for this case.

MFC after:	1 month
2013-11-09 21:24:56 +00:00
Pawel Jakub Dawidek
7008be5bd7 Change the cap_rights_t type from uint64_t to a structure that we can extend
in the future in a backward compatible (API and ABI) way.

The cap_rights_t represents capability rights. We used to use one bit to
represent one right, but we are running out of spare bits. Currently the new
structure provides place for 114 rights (so 50 more than the previous
cap_rights_t), but it is possible to grow the structure to hold at least 285
rights, although we can make it even larger if 285 rights won't be enough.

The structure definition looks like this:

	struct cap_rights {
		uint64_t	cr_rights[CAP_RIGHTS_VERSION + 2];
	};

The initial CAP_RIGHTS_VERSION is 0.

The top two bits in the first element of the cr_rights[] array contain total
number of elements in the array - 2. This means if those two bits are equal to
0, we have 2 array elements.

The top two bits in all remaining array elements should be 0.
The next five bits in all array elements contain array index. Only one bit is
used and bit position in this five-bits range defines array index. This means
there can be at most five array elements in the future.

To define new right the CAPRIGHT() macro must be used. The macro takes two
arguments - an array index and a bit to set, eg.

	#define	CAP_PDKILL	CAPRIGHT(1, 0x0000000000000800ULL)

We still support aliases that combine few rights, but the rights have to belong
to the same array element, eg:

	#define	CAP_LOOKUP	CAPRIGHT(0, 0x0000000000000400ULL)
	#define	CAP_FCHMOD	CAPRIGHT(0, 0x0000000000002000ULL)

	#define	CAP_FCHMODAT	(CAP_FCHMOD | CAP_LOOKUP)

There is new API to manage the new cap_rights_t structure:

	cap_rights_t *cap_rights_init(cap_rights_t *rights, ...);
	void cap_rights_set(cap_rights_t *rights, ...);
	void cap_rights_clear(cap_rights_t *rights, ...);
	bool cap_rights_is_set(const cap_rights_t *rights, ...);

	bool cap_rights_is_valid(const cap_rights_t *rights);
	void cap_rights_merge(cap_rights_t *dst, const cap_rights_t *src);
	void cap_rights_remove(cap_rights_t *dst, const cap_rights_t *src);
	bool cap_rights_contains(const cap_rights_t *big, const cap_rights_t *little);

Capability rights to the cap_rights_init(), cap_rights_set(),
cap_rights_clear() and cap_rights_is_set() functions are provided by
separating them with commas, eg:

	cap_rights_t rights;

	cap_rights_init(&rights, CAP_READ, CAP_WRITE, CAP_FSTAT);

There is no need to terminate the list of rights, as those functions are
actually macros that take care of the termination, eg:

	#define	cap_rights_set(rights, ...)				\
		__cap_rights_set((rights), __VA_ARGS__, 0ULL)
	void __cap_rights_set(cap_rights_t *rights, ...);

Thanks to using one bit as an array index we can assert in those functions that
there are no two rights belonging to different array elements provided
together. For example this is illegal and will be detected, because CAP_LOOKUP
belongs to element 0 and CAP_PDKILL to element 1:

	cap_rights_init(&rights, CAP_LOOKUP | CAP_PDKILL);

Providing several rights that belongs to the same array's element this way is
correct, but is not advised. It should only be used for aliases definition.

This commit also breaks compatibility with some existing Capsicum system calls,
but I see no other way to do that. This should be fine as Capsicum is still
experimental and this change is not going to 9.x.

Sponsored by:	The FreeBSD Foundation
2013-09-05 00:09:56 +00:00
Rick Macklem
f7d8291af0 Crashes have been observed for NFSv4.1 mounts when the system
is being shut down which were caused by the nfscbd_pool being
destroyed before the backchannel is disabled. This patch is
believed to fix the problem, by simply avoiding ever destroying
the nfscbd_pool. Since the NFS client module cannot be unloaded,
this should not cause a memory leak.

MFC after:	2 weeks
2013-09-04 22:47:56 +00:00
Rick Macklem
8fe6bddff7 Forced dismounts of NFS mounts can fail when thread(s) are stuck
waiting for an RPC reply from the server while holding the mount
point busy (mnt_lockref incremented). This happens because dounmount()
msleep()s waiting for mnt_lockref to become 0, before calling
VFS_UNMOUNT(). This patch adds a new VFS operation called VFS_PURGE(),
which the NFS client implements as purging RPCs in progress. Making
this call before checking mnt_lockref fixes the problem, by ensuring
that the VOP_xxx() calls will fail and unbusy the mount point.

Reported by:	sbruno
Reviewed by:	kib
MFC after:	2 weeks
2013-09-01 23:02:59 +00:00