cifs: use workqueue instead of slow-work

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>

1 files changed, 12 insertions, 8 deletions

diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index 1394aa37f26c..3ccadc1326d6 100644
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -498,7 +498,6 @@ is_valid_oplock_break(struct smb_hdr *buf, struct TCP_Server_Info *srv)
         struct cifsTconInfo *tcon;
         struct cifsInodeInfo *pCifsInode;
         struct cifsFileInfo *netfile;
-        int rc;
 
         cFYI(1, "Checking for oplock break or dnotify response");
         if ((pSMB->hdr.Command == SMB_COM_NT_TRANSACT) &&
@@ -583,13 +582,18 @@ is_valid_oplock_break(struct smb_hdr *buf, struct TCP_Server_Info *srv)
                                 pCifsInode->clientCanCacheAll = false;
                                 if (pSMB->OplockLevel == 0)
                                         pCifsInode->clientCanCacheRead = false;
-                                rc = slow_work_enqueue(&netfile->oplock_break);
-                                if (rc) {
-                                        cERROR(1, "failed to enqueue oplock "
-                                                   "break: %d\n", rc);
-                                } else {
-                                        netfile->oplock_break_cancelled = false;
-                                }
+
+                                /*
+                                 * cifs_oplock_break_put() can't be called
+                                 * from here.  Get reference after queueing
+                                 * succeeded.  cifs_oplock_break() will
+                                 * synchronize using GlobalSMSSeslock.
+                                 */
+                                if (queue_work(system_nrt_wq,
+                                               &netfile->oplock_break))
+                                        cifs_oplock_break_get(netfile);
+                                netfile->oplock_break_cancelled = false;
+
                                 read_unlock(&GlobalSMBSeslock);
                                 read_unlock(&cifs_tcp_ses_lock);
                                 return true;