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, 2 insertions, 2 deletions

diff --git a/fs/cifs/sess.c b/fs/cifs/sess.c
index e35dc60d3255..2a11efd96592 100644
--- a/fs/cifs/sess.c
+++ b/fs/cifs/sess.c
@@ -80,7 +80,7 @@ static __le16 get_next_vcnum(struct cifsSesInfo *ses)
         if (max_vcs < 2)
                 max_vcs = 0xFFFF;
 
-        write_lock(&cifs_tcp_ses_lock);
+        spin_lock(&cifs_tcp_ses_lock);
         if ((ses->need_reconnect) && is_first_ses_reconnect(ses))
                         goto get_vc_num_exit;  /* vcnum will be zero */
         for (i = ses->server->srv_count - 1; i < max_vcs; i++) {
@@ -112,7 +112,7 @@ static __le16 get_next_vcnum(struct cifsSesInfo *ses)
                 vcnum = i;
         ses->vcnum = vcnum;
 get_vc_num_exit:
-        write_unlock(&cifs_tcp_ses_lock);
+        spin_unlock(&cifs_tcp_ses_lock);
 
         return cpu_to_le16(vcnum);
 }