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, 7 insertions, 7 deletions

diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index de6073cccd9c..a7b492c213cd 100644
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -347,7 +347,7 @@ header_assemble(struct smb_hdr *buffer, char smb_command /* command */ ,
                                 if (current_fsuid() != treeCon->ses->linux_uid) {
                                         cFYI(1, "Multiuser mode and UID "
                                                  "did not match tcon uid");
-                                        read_lock(&cifs_tcp_ses_lock);
+                                        spin_lock(&cifs_tcp_ses_lock);
                                         list_for_each(temp_item, &treeCon->ses->server->smb_ses_list) {
                                                 ses = list_entry(temp_item, struct cifsSesInfo, smb_ses_list);
                                                 if (ses->linux_uid == current_fsuid()) {
@@ -361,7 +361,7 @@ header_assemble(struct smb_hdr *buffer, char smb_command /* command */ ,
                                                         }
                                                 }
                                         }
-                                        read_unlock(&cifs_tcp_ses_lock);
+                                        spin_unlock(&cifs_tcp_ses_lock);
                                 }
                         }
                 }
@@ -551,7 +551,7 @@ is_valid_oplock_break(struct smb_hdr *buf, struct TCP_Server_Info *srv)
                 return false;
 
         /* look up tcon based on tid & uid */
-        read_lock(&cifs_tcp_ses_lock);
+        spin_lock(&cifs_tcp_ses_lock);
         list_for_each(tmp, &srv->smb_ses_list) {
                 ses = list_entry(tmp, struct cifsSesInfo, smb_ses_list);
                 list_for_each(tmp1, &ses->tcon_list) {
@@ -573,7 +573,7 @@ is_valid_oplock_break(struct smb_hdr *buf, struct TCP_Server_Info *srv)
                                  */
                                 if (netfile->closePend) {
                                         spin_unlock(&cifs_file_list_lock);
-                                        read_unlock(&cifs_tcp_ses_lock);
+                                        spin_unlock(&cifs_tcp_ses_lock);
                                         return true;
                                 }
 
@@ -595,16 +595,16 @@ is_valid_oplock_break(struct smb_hdr *buf, struct TCP_Server_Info *srv)
                                 netfile->oplock_break_cancelled = false;
 
                                 spin_unlock(&cifs_file_list_lock);
-                                read_unlock(&cifs_tcp_ses_lock);
+                                spin_unlock(&cifs_tcp_ses_lock);
                                 return true;
                         }
                         spin_unlock(&cifs_file_list_lock);
-                        read_unlock(&cifs_tcp_ses_lock);
+                        spin_unlock(&cifs_tcp_ses_lock);
                         cFYI(1, "No matching file for oplock break");
                         return true;
                 }
         }
-        read_unlock(&cifs_tcp_ses_lock);
+        spin_unlock(&cifs_tcp_ses_lock);
         cFYI(1, "Can not process oplock break for non-existent connection");
         return true;
 }