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, 4 insertions, 4 deletions

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index f1d9c71e807..cb77915a445 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -482,16 +482,16 @@ static void cifs_umount_begin(struct super_block *sb)
 
         tcon = cifs_sb_master_tcon(cifs_sb);
 
-        read_lock(&cifs_tcp_ses_lock);
+        spin_lock(&cifs_tcp_ses_lock);
         if ((tcon->tc_count > 1) || (tcon->tidStatus == CifsExiting)) {
                 /* we have other mounts to same share or we have
                    already tried to force umount this and woken up
                    all waiting network requests, nothing to do */
-                read_unlock(&cifs_tcp_ses_lock);
+                spin_unlock(&cifs_tcp_ses_lock);
                 return;
         } else if (tcon->tc_count == 1)
                 tcon->tidStatus = CifsExiting;
-        read_unlock(&cifs_tcp_ses_lock);
+        spin_unlock(&cifs_tcp_ses_lock);
 
         /* cancel_brl_requests(tcon); */ /* BB mark all brl mids as exiting */
         /* cancel_notify_requests(tcon); */
@@ -940,7 +940,7 @@ init_cifs(void)
         GlobalTotalActiveXid = 0;
         GlobalMaxActiveXid = 0;
         memset(Local_System_Name, 0, 15);
-        rwlock_init(&cifs_tcp_ses_lock);
+        spin_lock_init(&cifs_tcp_ses_lock);
         spin_lock_init(&cifs_file_list_lock);
         spin_lock_init(&GlobalMid_Lock);