tracing/user_events: Remove user_ns walk for groups

During discussions it was suggested that user_ns is not a good place to
try to attach a tracing namespace. The current code has stubs to enable
that work that are very likely to change and incur a performance cost.

Remove the user_ns walk when creating a group and determining the system
name to use, since it's unlikely user_ns will be used in the future.

Link: https://lore.kernel.org/all/20230601-urenkel-holzofen-cd9403b9cadd@brauner/
Link: https://lore.kernel.org/linux-trace-kernel/20230601224928.301-1-beaub@linux.microsoft.com
Suggested-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 49914b6cb6517b2c90af7c6d7d4a80c0275cc050..cf6d4c02c363c85db6fd21702e36cea21a19962b 100644 (file)
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -182,21 +182,11 @@ static void user_event_group_destroy(struct user_event_group *group)
        kfree(group);
 }
 
-static char *user_event_group_system_name(struct user_namespace *user_ns)
+static char *user_event_group_system_name(void)
 {
        char *system_name;
        int len = sizeof(USER_EVENTS_SYSTEM) + 1;
 
-       if (user_ns != &init_user_ns) {
-               /*
-                * Unexpected at this point:
-                * We only currently support init_user_ns.
-                * When we enable more, this will trigger a failure so log.
-                */
-               pr_warn("user_events: Namespace other than init_user_ns!\n");
-               return NULL;
-       }
-
        system_name = kmalloc(len, GFP_KERNEL);
 
        if (!system_name)
@@ -207,34 +197,12 @@ static char *user_event_group_system_name(struct user_namespace *user_ns)
        return system_name;
 }
 
-static inline struct user_event_group
-*user_event_group_from_user_ns(struct user_namespace *user_ns)
-{
-       if (user_ns == &init_user_ns)
-               return init_group;
-
-       return NULL;
-}
-
 static struct user_event_group *current_user_event_group(void)
 {
-       struct user_namespace *user_ns = current_user_ns();
-       struct user_event_group *group = NULL;
-
-       while (user_ns) {
-               group = user_event_group_from_user_ns(user_ns);
-
-               if (group)
-                       break;
-
-               user_ns = user_ns->parent;
-       }
-
-       return group;
+       return init_group;
 }
 
-static struct user_event_group
-*user_event_group_create(struct user_namespace *user_ns)
+static struct user_event_group *user_event_group_create(void)
 {
        struct user_event_group *group;
 
@@ -243,7 +211,7 @@ static struct user_event_group
        if (!group)
                return NULL;
 
-       group->system_name = user_event_group_system_name(user_ns);
+       group->system_name = user_event_group_system_name();
 
        if (!group->system_name)
                goto error;
@@ -2603,7 +2571,7 @@ static int __init trace_events_user_init(void)
        if (!fault_cache)
                return -ENOMEM;
 
-       init_group = user_event_group_create(&init_user_ns);
+       init_group = user_event_group_create();
 
        if (!init_group) {
                kmem_cache_destroy(fault_cache);