slab: convert setup_slub_debug() to use __core_param_cb()

Use __core_param_cb() to parse the "slab_debug" kernel parameter instead of
the obsolescent __setup(). For now, the parameter is not exposed in sysfs,
and no get ops is provided.

There is a slight change in behavior. Before this patch, the following
parameter would silently turn on full debugging for all slabs:

  slub_debug_yada_yada_gotta_love_this=hail_satan!

This syntax is now rejected, and the parameter will be passed to user
space, making the kernel a holier place.

Signed-off-by: Petr Tesarik <ptesarik@suse.com>
Link: https://patch.msgid.link/9674b34861394088c7853edf8e9d2b439fd4b42f.1761324765.git.ptesarik@suse.com
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Author: ptesarik

mm/slub.c

@@ -1863,18 +1863,17 @@ parse_slub_debug_flags(const char *str, slab_flags_t *flags, const char **slabs,
 		return NULL;
 }
 
-static int __init setup_slub_debug(char *val)
+static int __init setup_slub_debug(const char *str, const struct kernel_param *kp)
 {
 	slab_flags_t flags;
 	slab_flags_t global_flags;
 	const char *saved_str;
 	const char *slab_list;
 	bool global_slub_debug_changed = false;
 	bool slab_list_specified = false;
-	const char *str = val;
 
 	global_flags = DEBUG_DEFAULT_FLAGS;
-	if (*str++ != '=' || !*str)
+	if (!str || !*str)
 		/*
 		 * No options specified. Switch on full debugging.
 		 */
@@ -1918,11 +1917,15 @@ static int __init setup_slub_debug(char *val)
 	     static_branch_unlikely(&init_on_free)) &&
 	    (slub_debug & SLAB_POISON))
 		pr_info("mem auto-init: SLAB_POISON will take precedence over init_on_alloc/init_on_free\n");
-	return 1;
+	return 0;
 }
 
-__setup("slab_debug", setup_slub_debug);
-__setup_param("slub_debug", slub_debug, setup_slub_debug, 0);
+static const struct kernel_param_ops param_ops_slab_debug __initconst = {
+	.flags = KERNEL_PARAM_OPS_FL_NOARG,
+	.set = setup_slub_debug,
+};
+__core_param_cb(slab_debug, &param_ops_slab_debug, NULL, 0);
+__core_param_cb(slub_debug, &param_ops_slab_debug, NULL, 0);
 
 /*
  * kmem_cache_flags - apply debugging options to the cache