netconsole: Add automatic console unregistration on target removal

Add unregister_netcons_consoles() function to automatically unregister
console handlers when no targets of the corresponding type remain active.

The function iterates through the target list to determine which console
types (basic vs extended) are still needed, and unregisters any console
handlers that are no longer required. This prevents having registered
console handlers without corresponding active targets.

The function is called when a target is disabled and moved to the cleanup
list, ensuring proper cleanup of unused console registrations.

Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20250609-netcons_ext-v3-2-5336fa670326@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 37 insertions, 2 deletions

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 01baa45221b4..21077aff061c 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -460,6 +460,33 @@ static ssize_t sysdata_release_enabled_show(struct config_item *item,
 	return sysfs_emit(buf, "%d\n", release_enabled);
 }
 
+/* Iterate in the list of target, and make sure we don't have any console
+ * register without targets of the same type
+ */
+static void unregister_netcons_consoles(void)
+{
+	struct netconsole_target *nt;
+	u32 console_type_needed = 0;
+	unsigned long flags;
+
+	spin_lock_irqsave(&target_list_lock, flags);
+	list_for_each_entry(nt, &target_list, list) {
+		if (nt->extended)
+			console_type_needed |= CONS_EXTENDED;
+		else
+			console_type_needed |= CONS_BASIC;
+	}
+	spin_unlock_irqrestore(&target_list_lock, flags);
+
+	if (!(console_type_needed & CONS_EXTENDED) &&
+	    console_is_registered(&netconsole_ext))
+		unregister_console(&netconsole_ext);
+
+	if (!(console_type_needed & CONS_BASIC) &&
+	    console_is_registered(&netconsole))
+		unregister_console(&netconsole);
+}
+
 /*
  * This one is special -- targets created through the configfs interface
  * are not enabled (and the corresponding netpoll activated) by default.
@@ -493,14 +520,18 @@ static ssize_t enabled_store(struct config_item *item,
 			goto out_unlock;
 		}
 
-		if (nt->extended && !console_is_registered(&netconsole_ext))
+		if (nt->extended && !console_is_registered(&netconsole_ext)) {
+			netconsole_ext.flags |= CON_ENABLED;
 			register_console(&netconsole_ext);
+		}
 
 		/* User might be enabling the basic format target for the very
 		 * first time, make sure the console is registered.
 		 */
-		if (!nt->extended && !console_is_registered(&netconsole))
+		if (!nt->extended && !console_is_registered(&netconsole)) {
+			netconsole.flags |= CON_ENABLED;
 			register_console(&netconsole);
+		}
 
 		/*
 		 * Skip netpoll_parse_options() -- all the attributes are
@@ -528,6 +559,10 @@ static ssize_t enabled_store(struct config_item *item,
 		list_move(&nt->list, &target_cleanup_list);
 		spin_unlock_irqrestore(&target_list_lock, flags);
 		mutex_unlock(&target_cleanup_list_lock);
+		/* Unregister consoles, whose the last target of that type got
+		 * disabled.
+		 */
+		unregister_netcons_consoles();
 	}
 
 	ret = strnlen(buf, count);