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, 13 insertions, 17 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 75541af4b3db..e767bfa7978b 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2295,8 +2295,7 @@ out:
         return rc;
 }
 
-static void
-cifs_oplock_break(struct slow_work *work)
+void cifs_oplock_break(struct work_struct *work)
 {
         struct cifsFileInfo *cfile = container_of(work, struct cifsFileInfo,
                                                   oplock_break);
@@ -2333,33 +2332,30 @@ cifs_oplock_break(struct slow_work *work)
                                  LOCKING_ANDX_OPLOCK_RELEASE, false);
                 cFYI(1, "Oplock release rc = %d", rc);
         }
+
+        /*
+         * We might have kicked in before is_valid_oplock_break()
+         * finished grabbing reference for us.  Make sure it's done by
+         * waiting for GlobalSMSSeslock.
+         */
+        write_lock(&GlobalSMBSeslock);
+        write_unlock(&GlobalSMBSeslock);
+
+        cifs_oplock_break_put(cfile);
 }
 
-static int
-cifs_oplock_break_get(struct slow_work *work)
+void cifs_oplock_break_get(struct cifsFileInfo *cfile)
 {
-        struct cifsFileInfo *cfile = container_of(work, struct cifsFileInfo,
-                                                  oplock_break);
         mntget(cfile->mnt);
         cifsFileInfo_get(cfile);
-        return 0;
 }
 
-static void
-cifs_oplock_break_put(struct slow_work *work)
+void cifs_oplock_break_put(struct cifsFileInfo *cfile)
 {
-        struct cifsFileInfo *cfile = container_of(work, struct cifsFileInfo,
-                                                  oplock_break);
         mntput(cfile->mnt);
         cifsFileInfo_put(cfile);
 }
 
-const struct slow_work_ops cifs_oplock_break_ops = {
-        .get_ref        = cifs_oplock_break_get,
-        .put_ref        = cifs_oplock_break_put,
-        .execute        = cifs_oplock_break,
-};
-
 const struct address_space_operations cifs_addr_ops = {
         .readpage = cifs_readpage,
         .readpages = cifs_readpages,