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, 6 insertions, 10 deletions

diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index 88786ba02d27..46c8c7baccba 100644
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -75,12 +75,11 @@ sesInfoAlloc(void)
 
         ret_buf = kzalloc(sizeof(struct cifsSesInfo), GFP_KERNEL);
         if (ret_buf) {
-                write_lock(&GlobalSMBSeslock);
                 atomic_inc(&sesInfoAllocCount);
                 ret_buf->status = CifsNew;
-                list_add(&ret_buf->cifsSessionList, &GlobalSMBSessionList);
+                ++ret_buf->ses_count;
+                INIT_LIST_HEAD(&ret_buf->smb_ses_list);
                 init_MUTEX(&ret_buf->sesSem);
-                write_unlock(&GlobalSMBSeslock);
         }
         return ret_buf;
 }
@@ -93,10 +92,7 @@ sesInfoFree(struct cifsSesInfo *buf_to_free)
                 return;
         }
 
-        write_lock(&GlobalSMBSeslock);
         atomic_dec(&sesInfoAllocCount);
-        list_del(&buf_to_free->cifsSessionList);
-        write_unlock(&GlobalSMBSeslock);
         kfree(buf_to_free->serverOS);
         kfree(buf_to_free->serverDomain);
         kfree(buf_to_free->serverNOS);
@@ -350,9 +346,9 @@ 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(&GlobalSMBSeslock);
-                                        list_for_each(temp_item, &GlobalSMBSessionList) {
-                                                ses = list_entry(temp_item, struct cifsSesInfo, cifsSessionList);
+                                        read_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) {
                                                         if (ses->server == treeCon->ses->server) {
                                                                 cFYI(1, ("found matching uid substitute right smb_uid"));
@@ -364,7 +360,7 @@ header_assemble(struct smb_hdr *buffer, char smb_command /* command */ ,
                                                         }
                                                 }
                                         }
-                                        read_unlock(&GlobalSMBSeslock);
+                                        read_unlock(&cifs_tcp_ses_lock);
                                 }
                         }
                 }