cifs: convert cifs_tcp_ses_lock from a rwlock to a spinlock

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>

1 files changed, 3 insertions, 3 deletions

diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index bfb59a68e4fd..e98f1f317b15 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -593,9 +593,9 @@ CIFSSMBNegotiate(unsigned int xid, struct cifsSesInfo *ses)
                         rc = -EIO;
                         goto neg_err_exit;
                 }
-                read_lock(&cifs_tcp_ses_lock);
+                spin_lock(&cifs_tcp_ses_lock);
                 if (server->srv_count > 1) {
-                        read_unlock(&cifs_tcp_ses_lock);
+                        spin_unlock(&cifs_tcp_ses_lock);
                         if (memcmp(server->server_GUID,
                                    pSMBr->u.extended_response.
                                    GUID, 16) != 0) {
@@ -605,7 +605,7 @@ CIFSSMBNegotiate(unsigned int xid, struct cifsSesInfo *ses)
                                         16);
                         }
                 } else {
-                        read_unlock(&cifs_tcp_ses_lock);
+                        spin_unlock(&cifs_tcp_ses_lock);
                         memcpy(server->server_GUID,
                                pSMBr->u.extended_response.GUID, 16);
                 }