Commit 743162013d ("sched: Remove proliferation of wait_on_bit() action
functions") has removed the call to cifs_oplock_break_wait, making this
function unused; remove it.
This fixes the following compilation warning:
fs/cifs/misc.c:578:1: warning: ‘cifs_oplock_break_wait’ defined but not used [-Wunused-function]
Signed-off-by: Vincent Stehlé <vincent.stehle@laposte.net>
Cc: Steve French <sfrench@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>
Pull CIFS updates from Steve French:
"The most visible change in this set is the additional of multi-credit
support for SMB2/SMB3 which dramatically improves the large file i/o
performance for these dialects and significantly increases the maximum
i/o size used on the wire for SMB2/SMB3.
Also reconnection behavior after network failure is improved"
* 'for-next' of git://git.samba.org/sfrench/cifs-2.6: (35 commits)
Add worker function to set allocation size
[CIFS] Fix incorrect hex vs. decimal in some debug print statements
update CIFS TODO list
Add Pavel to contributor list in cifs AUTHORS file
Update cifs version
CIFS: Fix STATUS_CANNOT_DELETE error mapping for SMB2
CIFS: Optimize readpages in a short read case on reconnects
CIFS: Optimize cifs_user_read() in a short read case on reconnects
CIFS: Improve indentation in cifs_user_read()
CIFS: Fix possible buffer corruption in cifs_user_read()
CIFS: Count got bytes in read_into_pages()
CIFS: Use separate var for the number of bytes got in async read
CIFS: Indicate reconnect with ECONNABORTED error code
CIFS: Use multicredits for SMB 2.1/3 reads
CIFS: Fix rsize usage for sync read
CIFS: Fix rsize usage in user read
CIFS: Separate page reading from user read
CIFS: Fix rsize usage in readpages
CIFS: Separate page search from readpages
CIFS: Use multicredits for SMB 2.1/3 writes
...
Joe Perches and Hans Wennborg noticed that various places in the
kernel were printing decimal numbers with 0x prefix.
printk("0x%d") or equivalent
This fixes the instances of this in the cifs driver.
CC: Hans Wennborg <hans@hanshq.net>
CC: Joe Perches <joe@perches.com>
Signed-off-by: Steve French <smfrench@gmail.com>
The functionality provided by free_rsp_buf() is duplicated in a number
of places. Replace these instances with a call to free_rsp_buf().
Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Reviewed-by: Shirish Pargaonkar <spargaonkar@suse.com>
Signed-off-by: Steve French <smfrench@gmail.com>
The current "wait_on_bit" interface requires an 'action'
function to be provided which does the actual waiting.
There are over 20 such functions, many of them identical.
Most cases can be satisfied by one of just two functions, one
which uses io_schedule() and one which just uses schedule().
So:
Rename wait_on_bit and wait_on_bit_lock to
wait_on_bit_action and wait_on_bit_lock_action
to make it explicit that they need an action function.
Introduce new wait_on_bit{,_lock} and wait_on_bit{,_lock}_io
which are *not* given an action function but implicitly use
a standard one.
The decision to error-out if a signal is pending is now made
based on the 'mode' argument rather than being encoded in the action
function.
All instances of the old wait_on_bit and wait_on_bit_lock which
can use the new version have been changed accordingly and their
action functions have been discarded.
wait_on_bit{_lock} does not return any specific error code in the
event of a signal so the caller must check for non-zero and
interpolate their own error code as appropriate.
The wait_on_bit() call in __fscache_wait_on_invalidate() was
ambiguous as it specified TASK_UNINTERRUPTIBLE but used
fscache_wait_bit_interruptible as an action function.
David Howells confirms this should be uniformly
"uninterruptible"
The main remaining user of wait_on_bit{,_lock}_action is NFS
which needs to use a freezer-aware schedule() call.
A comment in fs/gfs2/glock.c notes that having multiple 'action'
functions is useful as they display differently in the 'wchan'
field of 'ps'. (and /proc/$PID/wchan).
As the new bit_wait{,_io} functions are tagged "__sched", they
will not show up at all, but something higher in the stack. So
the distinction will still be visible, only with different
function names (gds2_glock_wait versus gfs2_glock_dq_wait in the
gfs2/glock.c case).
Since first version of this patch (against 3.15) two new action
functions appeared, on in NFS and one in CIFS. CIFS also now
uses an action function that makes the same freezer aware
schedule call as NFS.
Signed-off-by: NeilBrown <neilb@suse.de>
Acked-by: David Howells <dhowells@redhat.com> (fscache, keys)
Acked-by: Steven Whitehouse <swhiteho@redhat.com> (gfs2)
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steve French <sfrench@samba.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140707051603.28027.72349.stgit@notabene.brown
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Problem reported in Red Hat bz 1040329 for strict writes where we cache
only when we hold oplock and write direct to the server when we don't.
When we receive an oplock break, we first change the oplock value for
the inode in cifsInodeInfo->oplock to indicate that we no longer hold
the oplock before we enqueue a task to flush changes to the backing
device. Once we have completed flushing the changes, we return the
oplock to the server.
There are 2 ways here where we can have data corruption
1) While we flush changes to the backing device as part of the oplock
break, we can have processes write to the file. These writes check for
the oplock, find none and attempt to write directly to the server.
These direct writes made while we are flushing from cache could be
overwritten by data being flushed from the cache causing data
corruption.
2) While a thread runs in cifs_strict_writev, the machine could receive
and process an oplock break after the thread has checked the oplock and
found that it allows us to cache and before we have made changes to the
cache. In that case, we end up with a dirty page in cache when we
shouldn't have any. This will be flushed later and will overwrite all
subsequent writes to the part of the file represented by this page.
Before making any writes to the server, we need to confirm that we are
not in the process of flushing data to the server and if we are, we
should wait until the process is complete before we attempt the write.
We should also wait for existing writes to complete before we process
an oplock break request which changes oplock values.
We add a version specific downgrade_oplock() operation to allow for
differences in the oplock values set for the different smb versions.
Cc: stable@vger.kernel.org
Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <smfrench@gmail.com>
The multiplex identifier (MID) in the SMB header is only
ever used by the client, in conjunction with PID, to match responses
from the server. As such, the endianess of the MID is not important.
However, When tracing packet sequences on the wire, protocol analyzers
such as wireshark display MID as little endian. It is much more informative
for the on-the-wire MID sequences to match debug information emitted by the
CIFS driver. Therefore, one should write and read MID in the SMB header
assuming it is always little endian.
Observed from wireshark during the protocol negotiation
and session setup:
Multiplex ID: 256
Multiplex ID: 256
Multiplex ID: 512
Multiplex ID: 512
Multiplex ID: 768
Multiplex ID: 768
After this patch on-the-wire MID values begin at 1 and increase monotonically.
Introduce get_next_mid64() for the internal consumers that use the full 64 bit
multiplex identifier.
Introduce the helpers get_mid() and compare_mid() to make the endian
translation clear.
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Tim Gardner <timg@tpi.com>
Signed-off-by: Steve French <smfrench@gmail.com>
The only call site for check_smb_header() assigns 'mid' from the SMB
packet, which is then checked again in check_smb_header(). This seems
like redundant redundancy.
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Tim Gardner <timg@tpi.com>
Signed-off-by: Steve French <smfrench@gmail.com>
that prepare the code to handle different types of SMB2 leases.
Signed-off-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>
Move the post (successful) session setup code to respective dialect routines.
For smb1, session key is per smb connection.
For smb2/smb3, session key is per smb session.
If client and server do not require signing, free session key for smb1/2/3.
If client and server require signing
smb1 - Copy (kmemdup) session key for the first session to connection.
Free session key of that and subsequent sessions on this connection.
smb2 - For every session, keep the session key and free it when the
session is being shutdown.
smb3 - For every session, generate the smb3 signing key using the session key
and then free the session key.
There are two unrelated line formatting changes as well.
Reviewed-by: Jeff Layton <jlayton@samba.org>
Signed-off-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Currently, we determine this according to flags in the sec_mode, flags
in the global_secflags and via other methods. That makes the semantics
very hard to follow and there are corner cases where we don't handle
this correctly.
Add a new bool to the TCP_Server_Info that acts as a simple flag to tell
us whether signing is enabled on this connection or not, and fix up the
places that need to determine this to use that flag.
This is a bit weird for the SMB2 case, where signing is per-session.
SMB2 needs work in this area already though. The existing SMB2 code has
similar logic to what we're using here, so there should be no real
change in behavior. These changes should make it easier to implement
per-session signing in the future though.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <smfrench@gmail.com>
It's not obvious from reading the macro names that these macros
are for debugging. Convert the names to a single more typical
kernel style cifs_dbg macro.
cERROR(1, ...) -> cifs_dbg(VFS, ...)
cFYI(1, ...) -> cifs_dbg(FYI, ...)
cFYI(DBG2, ...) -> cifs_dbg(NOISY, ...)
Move the terminating format newline from the macro to the call site.
Add CONFIG_CIFS_DEBUG function cifs_vfs_err to emit the
"CIFS VFS: " prefix for VFS messages.
Size is reduced ~ 1% when CONFIG_CIFS_DEBUG is set (default y)
$ size fs/cifs/cifs.ko*
text data bss dec hex filename
265245 2525 132 267902 4167e fs/cifs/cifs.ko.new
268359 2525 132 271016 422a8 fs/cifs/cifs.ko.old
Other miscellaneous changes around these conversions:
o Miscellaneous typo fixes
o Add terminating \n's to almost all formats and remove them
from the macros to be more kernel style like. A few formats
previously had defective \n's
o Remove unnecessary OOM messages as kmalloc() calls dump_stack
o Coalesce formats to make grep easier,
added missing spaces when coalescing formats
o Use %s, __func__ instead of embedded function name
o Removed unnecessary "cifs: " prefixes
o Convert kzalloc with multiply to kcalloc
o Remove unused cifswarn macro
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Now we walk though cifsFileInfo's list for every incoming lease
break and look for an equivalent there. That approach misses lease
breaks that come just after an open response - we don't have time
to populate new cifsFileInfo structure to the list. Fix this by
adding new list of pending opens and look for a lease there if we
didn't find it in the list of cifsFileInfo structures.
Signed-off-by: Pavel Shilovsky <pshilovsky@etersoft.ru>
Signed-off-by: Steve French <sfrench@us.ibm.com>
This is help us to extend the code for future protocols that can use
another fid mechanism (as SMB2 that has it divided into two parts:
persistent and violatile).
Also rename variables and refactor the code around the changes.
Reviewed-by: Jeff Layton <jlayton@samba.org>
Signed-off-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Steve French <smfrench@gmail.com>
Use SMB2 header size values for allocation and memset because they
are bigger and suitable for both CIFS and SMB2.
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <smfrench@gmail.com>
Acked-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <sfrench@us.ibm.com>
...and convert existing cifs users of system_nrt_wq to use that instead.
Also, make it freezable, and set WQ_MEM_RECLAIM since we use it to
deal with write reply handling.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Acked-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
While in CIFS/SMB we have 16 bit mid, in SMB2 it is 64 bit.
Convert the existing field to 64 bit and mask off higher bits
for CIFS/SMB.
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
and send no more than credits value requests at once. For SMB/CIFS
it's trivial: increment this value by receiving any message and
decrement by sending one.
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <sfrench@us.ibm.com>
Add mount options backupuid and backugid.
It allows an authenticated user to access files with the intent to back them
up including their ACLs, who may not have access permission but has
"Backup files and directories user right" on them (by virtue of being part
of the built-in group Backup Operators.
When mount options backupuid is specified, cifs client restricts the
use of backup intents to the user whose effective user id is specified
along with the mount option.
When mount options backupgid is specified, cifs client restricts the
use of backup intents to the users whose effective user id belongs to the
group id specified along with the mount option.
If an authenticated user is not part of the built-in group Backup Operators
at the server, access to such files is denied, even if allowed by the client.
Signed-off-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
The variable names in this function are so ambiguous that it's very
difficult to know what it's doing. Rename them to make it a bit more
clear.
Also, remove a redundant length check. cifsd checks to make sure that
the rfclen isn't larger than the maximum frame size when it does the
receive.
Finally, change checkSMB to return a real error code (-EIO) when
it finds an error. That will help simplify some coming changes in the
callers.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Currently, we take a sb->s_active reference and a cifsFileInfo reference
when an oplock break workqueue job is queued. This is unnecessary and
more complicated than it needs to be. Also as Al points out,
deactivate_super has non-trivial locking implications so it's best to
avoid that if we can.
Instead, just cancel any pending oplock breaks for this filehandle
synchronously in cifsFileInfo_put after taking it off the lists.
That should ensure that this job doesn't outlive the structures it
depends on.
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
This is the same patch as originally posted, just with some merge
conflicts fixed up...
Currently, the ByteCount is usually converted to host-endian on receive.
This is confusing however, as we need to keep two sets of routines for
accessing it, and keep track of when to use each routine. Munging
received packets like this also limits when the signature can be
calulated.
Simplify the code by keeping the received ByteCount in little-endian
format. This allows us to eliminate a set of routines for accessing it
and we can now drop the *_le suffixes from the accessor functions since
that's now implied.
While we're at it, switch all of the places that read the ByteCount
directly to use the get_bcc inline which should also clean up some
unaligned accesses.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
There is one big endian field in the cifs protocol, the RFC1001
length, which cifs code (unlike in the smb2 code) had been handling as
u32 until the last possible moment, when it was converted to be32 (its
native form) before sending on the wire. To remove the last sparse
endian warning, and to make this consistent with the smb2
implementation (which always treats the fields in their
native size and endianness), convert all uses of smb_buf_length to
be32.
This version incorporates Christoph's comment about
using be32_add_cpu, and fixes a typo in the second
version of the patch.
Signed-off-by: Steve French <sfrench@us.ibm.com>
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <sfrench@us.ibm.com>
The BCC is still __le16 at this point, and in any case we need to
use the get_bcc_le macro to make sure we don't hit alignment
problems.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
We artificially limited the user name to 32 bytes, but modern servers handle
larger. Set the maximum length to a reasonable 256, and make the user name
string dynamically allocated rather than a fixed size in session structure.
Also clean up old checkpatch warning.
Signed-off-by: Steve French <sfrench@us.ibm.com>
The cERROR message in checkSMB when the calculated length doesn't match
the RFC1001 length is incorrect in many cases. It always says that the
RFC1001 length is bigger than the SMB, even when it's actually the
reverse.
Fix the error message to say the reverse of what it does now when the
SMB length goes beyond the end of the received data. Also, clarify the
error message when the RFC length is too big. Finally, clarify the
comments to show that the 512 byte limit on extra data at the end of
the packet is arbitrary.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
Currently, we allow the pending_mid_q to grow without bound with
SIGKILL'ed processes. This could eventually be a DoS'able problem. An
unprivileged user could a process that does a long-running call and then
SIGKILL it.
If he can also intercept the NT_CANCEL calls or the replies from the
server, then the pending_mid_q could grow very large, possibly even to
2^16 entries which might leave GetNextMid in an infinite loop. Fix this
by imposing a hard limit of 32k calls per server. If we cross that
limit, set the tcpStatus to CifsNeedReconnect to force cifsd to
eventually reconnect the socket and clean out the pending_mid_q.
While we're at it, clean up the function a bit and eliminate an
unnecessary NULL pointer check.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
...just cleanup. There should be no behavior change.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Pavel Shilovsky <piastryyy@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
Move cifsConvertToUCS to cifs_unicode.c where all of the other unicode
related functions live. Have it store mapped characters in 'temp' and
then use put_unaligned_le16 to copy it to the target buffer. Also fix
the comments to match kernel coding style.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Acked-by: Pavel Shilovsky <piastryyy@gmail.com>
Reviewed-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
When we get oplock break notification we should set the appropriate
value of OplockLevel field in oplock break acknowledge according to
the oplock level held by the client in this time. As we only can have
level II oplock or no oplock in the case of oplock break, we should be
aware only about clientCanCacheRead field in cifsInodeInfo structure.
Also fix bug connected with wrong interpretation of OplockLevel field
during oplock break notification processing.
Signed-off-by: Pavel Shilovsky <piastryyy@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Steve French <sfrench@us.ibm.com>
All the callers already have a pointer to struct cifsInodeInfo. Use it.
Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
Signed-off-by: Pavel Shilovsky <piastryyy@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
Simplify many places when we need to set oplock level on an inode.
Signed-off-by: Pavel Shilovsky <piastryyy@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
GlobalSMBSesLock is now cifs_file_list_lock. Update comments to reflect this.
Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
Signed-off-by: Steve French <sfrench@us.ibm.com>
Now that it's feasible for a cifsFileInfo to outlive the filp under
which it was created, move the close processing into cifsFileInfo_put.
This means that the last user of the filehandle always does the actual
on the wire close call. This also allows us to get rid of the closePend
flag from cifsFileInfo. If we have an active reference to the file
then it's never going to have a close pending.
cifs_close is converted to simply put the filehandle.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Suresh Jayaraman <sjayaraman@suse.de>
Signed-off-by: Steve French <sfrench@us.ibm.com>
cifs_tcp_ses_lock is a rwlock with protects the cifs_tcp_ses_list,
server->smb_ses_list and the ses->tcon_list. It also protects a few
ref counters in server, ses and tcon. In most cases the critical section
doesn't seem to be large, in a few cases where it is slightly large, there
seem to be really no benefit from concurrent access. I briefly considered RCU
mechanism but it appears to me that there is no real need.
Replace it with a spinlock and get rid of the last rwlock in the cifs code.
Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
Signed-off-by: Steve French <sfrench@us.ibm.com>
Convert this lock to a regular spinlock
A rwlock_t offers little value here. It's more expensive than a regular
spinlock unless you have a fairly large section of code that runs under
the read lock and can benefit from the concurrency.
Additionally, we need to ensure that the refcounting for files isn't
racy and to do that we need to lock areas that can increment it for
write. That means that the areas that can actually use a read_lock are
very few and relatively infrequently used.
While we're at it, change the name to something easier to type, and fix
a bug in find_writable_file. cifsFileInfo_put can sleep and shouldn't be
called while holding the lock.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Suresh Jayaraman <sjayaraman@suse.de>
Signed-off-by: Steve French <sfrench@us.ibm.com>
cifsFileInfo is a bit problematic. It contains a reference back to the
struct file itself. This makes it difficult for a cifsFileInfo to exist
without a corresponding struct file.
It would be better instead of the cifsFileInfo just held info pertaining
to the open file on the server instead without any back refrences to the
struct file. This would allow it to exist after the filp to which it was
originally attached was closed.
Much of the use of the file pointer in this struct is to get at the
dentry. Begin divorcing the cifsFileInfo from the struct file by
keeping a reference to the dentry. Since the dentry will have a
reference to the inode, we can eliminate the "pInode" field too and
convert the igrab/iput to dget/dput.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Suresh Jayaraman <sjayaraman@suse.de>
Acked-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
At mount time, we'll always need to create a tcon that will serve as a
template for others that are associated with the mount. This tcon is
known as the "master" tcon.
In some cases, we'll need to use that tcon regardless of who's accessing
the mount. Add an accessor function for the master tcon and go ahead and
switch the appropriate places to use it.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
When we convert cifs to do multiple sessions per mount, we'll need more
than one tcon per superblock. At that point "cifs_sb->tcon" will make
no sense. Add a new accessor function that gets a tcon given a cifs_sb.
For now, it just returns cifs_sb->tcon. Later it'll do more.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
Workqueue can now handle high concurrency. Use system_nrt_wq
instead of slow-work.
* Updated is_valid_oplock_break() to not call cifs_oplock_break_put()
as advised by Steve French. It might cause deadlock. Instead,
reference is increased after queueing succeeded and
cifs_oplock_break() briefly grabs GlobalSMBSeslock before putting
the cfile to make sure it doesn't put before the matching get is
finished.
* Anton Blanchard reported that cifs conversion was using now gone
system_single_wq. Use system_nrt_wq which provides non-reentrance
guarantee which is enough and much better.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Steve French <sfrench@samba.org>
Cc: Anton Blanchard <anton@samba.org>
Vincent Stehlé