cifs: reinstate sharing of SMB sessions sans races

We do this by abandoning the global list of SMB sessions and instead
moving to a per-server list. This entails adding a new list head to the
TCP_Server_Info struct. The refcounting for the cifsSesInfo is moved to
a non-atomic variable. We have to protect it by a lock anyway, so there's
no benefit to making it an atomic. The list and refcount are protected
by the global cifs_tcp_ses_lock.

The patch also adds a new routines to find and put SMB sessions and
that properly take and put references under the lock.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 7 insertions, 15 deletions

diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index cd9e9a145e4d..9c95617baa4d 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -799,20 +799,16 @@ CIFSSMBLogoff(const int xid, struct cifsSesInfo *ses)
         int rc = 0;
 
         cFYI(1, ("In SMBLogoff for session disconnect"));
-        if (ses)
-                down(&ses->sesSem);
-        else
-                return -EIO;
-
-        atomic_dec(&ses->inUse);
-        if (atomic_read(&ses->inUse) > 0) {
-                up(&ses->sesSem);
-                return -EBUSY;
-        }
 
-        if (ses->server == NULL)
+        /*
+         * BB: do we need to check validity of ses and server? They should
+         * always be valid since we have an active reference. If not, that
+         * should probably be a BUG()
+         */
+        if (!ses || !ses->server)
                 return -EIO;
 
+        down(&ses->sesSem);
         if (ses->need_reconnect)
                 goto session_already_dead; /* no need to send SMBlogoff if uid
                                               already closed due to reconnect */
@@ -833,10 +829,6 @@ CIFSSMBLogoff(const int xid, struct cifsSesInfo *ses)
         pSMB->AndXCommand = 0xFF;
         rc = SendReceiveNoRsp(xid, ses, (struct smb_hdr *) pSMB, 0);
 session_already_dead:
-        if (ses->server) {
-                cifs_put_tcp_session(ses->server);
-                rc = 0;
-        }
         up(&ses->sesSem);
 
         /* if session dead then we do not need to do ulogoff,