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;