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>

fs/cifs/cifs_debug.c

@@ -107,9 +107,9 @@ void cifs_dump_mids(struct TCP_Server_Info *server)
 #ifdef CONFIG_PROC_FS
 static int cifs_debug_data_proc_show(struct seq_file *m, void *v)
 {
-	struct list_head *tmp;
-	struct list_head *tmp1;
+	struct list_head *tmp, *tmp2, *tmp3;
 	struct mid_q_entry *mid_entry;
+	struct TCP_Server_Info *server;
 	struct cifsSesInfo *ses;
 	struct cifsTconInfo *tcon;
 	int i;
@@ -122,43 +122,45 @@ static int cifs_debug_data_proc_show(struct seq_file *m, void *v)
 	seq_printf(m, "Servers:");
 
 	i = 0;
-	read_lock(&GlobalSMBSeslock);
-	list_for_each(tmp, &GlobalSMBSessionList) {
+	read_lock(&cifs_tcp_ses_lock);
+	list_for_each(tmp, &cifs_tcp_ses_list) {
+		server = list_entry(tmp, struct TCP_Server_Info,
+				    tcp_ses_list);
 		i++;
-		ses = list_entry(tmp, struct cifsSesInfo, cifsSessionList);
-		if ((ses->serverDomain == NULL) || (ses->serverOS == NULL) ||
-		   (ses->serverNOS == NULL)) {
-			seq_printf(m, "\nentry for %s not fully "
-					"displayed\n\t", ses->serverName);
-		} else {
-			seq_printf(m,
+		list_for_each(tmp2, &server->smb_ses_list) {
+			ses = list_entry(tmp2, struct cifsSesInfo,
+					 smb_ses_list);
+			if ((ses->serverDomain == NULL) ||
+				(ses->serverOS == NULL) ||
+				(ses->serverNOS == NULL)) {
+				seq_printf(m, "\nentry for %s not fully "
+					   "displayed\n\t", ses->serverName);
+			} else {
+				seq_printf(m,
 				    "\n%d) Name: %s  Domain: %s Mounts: %d OS:"
 				    " %s  \n\tNOS: %s\tCapability: 0x%x\n\tSMB"
 				    " session status: %d\t",
 				i, ses->serverName, ses->serverDomain,
-				atomic_read(&ses->inUse),
-				ses->serverOS, ses->serverNOS,
+				ses->ses_count, ses->serverOS, ses->serverNOS,
 				ses->capabilities, ses->status);
-		}
-		if (ses->server) {
+			}
 			seq_printf(m, "TCP status: %d\n\tLocal Users To "
-				    "Server: %d SecMode: 0x%x Req On Wire: %d",
-				ses->server->tcpStatus,
-				ses->server->srv_count,
-				ses->server->secMode,
-				atomic_read(&ses->server->inFlight));
+				   "Server: %d SecMode: 0x%x Req On Wire: %d",
+				   server->tcpStatus, server->srv_count,
+				   server->secMode,
+				   atomic_read(&server->inFlight));
 
 #ifdef CONFIG_CIFS_STATS2
 			seq_printf(m, " In Send: %d In MaxReq Wait: %d",
-				atomic_read(&ses->server->inSend),
-				atomic_read(&ses->server->num_waiters));
+				atomic_read(&server->inSend),
+				atomic_read(&server->num_waiters));
 #endif
 
 			seq_puts(m, "\nMIDs:\n");
 
 			spin_lock(&GlobalMid_Lock);
-			list_for_each(tmp1, &ses->server->pending_mid_q) {
-				mid_entry = list_entry(tmp1, struct
+			list_for_each(tmp3, &server->pending_mid_q) {
+				mid_entry = list_entry(tmp3, struct
 					mid_q_entry,
 					qhead);
 				seq_printf(m, "State: %d com: %d pid:"
@@ -171,9 +173,8 @@ static int cifs_debug_data_proc_show(struct seq_file *m, void *v)
 			}
 			spin_unlock(&GlobalMid_Lock);
 		}
-
 	}
-	read_unlock(&GlobalSMBSeslock);
+	read_unlock(&cifs_tcp_ses_lock);
 	seq_putc(m, '\n');
 
 	seq_puts(m, "Shares:");

fs/cifs/cifsfs.c

@@ -1031,24 +1031,24 @@ static int cifs_oplock_thread(void *dummyarg)
 static int cifs_dnotify_thread(void *dummyarg)
 {
 	struct list_head *tmp;
-	struct cifsSesInfo *ses;
+	struct TCP_Server_Info *server;
 
 	do {
 		if (try_to_freeze())
 			continue;
 		set_current_state(TASK_INTERRUPTIBLE);
 		schedule_timeout(15*HZ);
-		read_lock(&GlobalSMBSeslock);
 		/* check if any stuck requests that need
 		   to be woken up and wakeq so the
 		   thread can wake up and error out */
-		list_for_each(tmp, &GlobalSMBSessionList) {
-			ses = list_entry(tmp, struct cifsSesInfo,
-				cifsSessionList);
-			if (ses->server && atomic_read(&ses->server->inFlight))
-				wake_up_all(&ses->server->response_q);
+		read_lock(&cifs_tcp_ses_lock);
+		list_for_each(tmp, &cifs_tcp_ses_list) {
+			server = list_entry(tmp, struct TCP_Server_Info,
+					 tcp_ses_list);
+			if (atomic_read(&server->inFlight))
+				wake_up_all(&server->response_q);
 		}
-		read_unlock(&GlobalSMBSeslock);
+		read_unlock(&cifs_tcp_ses_lock);
 	} while (!kthread_should_stop());
 
 	return 0;
@@ -1060,7 +1060,6 @@ init_cifs(void)
 	int rc = 0;
 	cifs_proc_init();
 	INIT_LIST_HEAD(&cifs_tcp_ses_list);
-	INIT_LIST_HEAD(&GlobalSMBSessionList); /* BB to be removed by jl */
 	INIT_LIST_HEAD(&GlobalTreeConnectionList); /* BB to be removed by jl */
 	INIT_LIST_HEAD(&GlobalOplock_Q);
 #ifdef CONFIG_CIFS_EXPERIMENTAL

fs/cifs/cifsglob.h

@@ -195,14 +195,14 @@ struct cifsUidInfo {
  * Session structure.  One of these for each uid session with a particular host
  */
 struct cifsSesInfo {
-	struct list_head cifsSessionList;
+	struct list_head smb_ses_list;
 	struct list_head tcon_list;
 	struct semaphore sesSem;
 #if 0
 	struct cifsUidInfo *uidInfo;	/* pointer to user info */
 #endif
 	struct TCP_Server_Info *server;	/* pointer to server info */
-	atomic_t inUse; /* # of mounts (tree connections) on this ses */
+	int ses_count;		/* reference counter */
 	enum statusEnum status;
 	unsigned overrideSecFlg;  /* if non-zero override global sec flags */
 	__u16 ipc_tid;		/* special tid for connection to IPC share */
@@ -602,8 +602,6 @@ GLOBAL_EXTERN struct list_head		cifs_tcp_ses_list;
 
 /* protects cifs_tcp_ses_list and srv_count for each tcp session */
 GLOBAL_EXTERN rwlock_t		cifs_tcp_ses_lock;
-
-GLOBAL_EXTERN struct list_head GlobalSMBSessionList; /* BB to be removed by jl*/
 GLOBAL_EXTERN struct list_head GlobalTreeConnectionList; /* BB to be removed */
 GLOBAL_EXTERN rwlock_t GlobalSMBSeslock;  /* protects list inserts on 3 above */
 

fs/cifs/cifsproto.h

@@ -102,7 +102,6 @@ extern void acl_to_uid_mode(struct inode *inode, const char *path,
 			    const __u16 *pfid);
 extern int mode_to_acl(struct inode *inode, const char *path, __u64);
 
-extern void cifs_put_tcp_session(struct TCP_Server_Info *server);
 extern int cifs_mount(struct super_block *, struct cifs_sb_info *, char *,
 			const char *);
 extern int cifs_umount(struct super_block *, struct cifs_sb_info *);

fs/cifs/cifssmb.c

@@ -799,20 +799,16 @@ CIFSSMBLogoff(const int xid, struct cifsSesInfo *ses)
 	int rc = 0;
 
 	cFYI(1, ("In SMBLogoff for session disconnect"));
-	if (ses)
-		down(&ses->sesSem);
-	else
-		return -EIO;
-
-	atomic_dec(&ses->inUse);
-	if (atomic_read(&ses->inUse) > 0) {
-		up(&ses->sesSem);
-		return -EBUSY;
-	}
 
-	if (ses->server == NULL)
+	/*
+	 * BB: do we need to check validity of ses and server? They should
+	 * always be valid since we have an active reference. If not, that
+	 * should probably be a BUG()
+	 */
+	if (!ses || !ses->server)
 		return -EIO;
 
+	down(&ses->sesSem);
 	if (ses->need_reconnect)
 		goto session_already_dead; /* no need to send SMBlogoff if uid
 					      already closed due to reconnect */
@@ -833,10 +829,6 @@ CIFSSMBLogoff(const int xid, struct cifsSesInfo *ses)
 	pSMB->AndXCommand = 0xFF;
 	rc = SendReceiveNoRsp(xid, ses, (struct smb_hdr *) pSMB, 0);
 session_already_dead:
-	if (ses->server) {
-		cifs_put_tcp_session(ses->server);
-		rc = 0;
-	}
 	up(&ses->sesSem);
 
 	/* if session dead then we do not need to do ulogoff,

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);
 				}
 			}
 		}