mm: Move mm_cachep initialization to mm_init()

In order to allow using mm_alloc() much earlier, move initializing
mm_cachep into mm_init().
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20221025201057.751153381@infradead.org

include/linux/sched/task.h

@@ -65,6 +65,7 @@ extern void sched_dead(struct task_struct *p);
 void __noreturn do_task_dead(void);
 void __noreturn make_task_dead(int signr);
 
+extern void mm_cache_init(void);
 extern void proc_caches_init(void);
 
 extern void fork_init(void);

init/main.c

@@ -860,6 +860,7 @@ static void __init mm_init(void)
 	/* Should be run after espfix64 is set up. */
 	pti_init();
 	kmsan_init_runtime();
+	mm_cache_init();
 }
 
 #ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET

kernel/fork.c

@@ -3015,10 +3015,27 @@ static void sighand_ctor(void *data)
 	init_waitqueue_head(&sighand->signalfd_wqh);
 }
 
-void __init proc_caches_init(void)
+void __init mm_cache_init(void)
 {
 	unsigned int mm_size;
 
+	/*
+	 * The mm_cpumask is located at the end of mm_struct, and is
+	 * dynamically sized based on the maximum CPU number this system
+	 * can have, taking hotplug into account (nr_cpu_ids).
+	 */
+	mm_size = sizeof(struct mm_struct) + cpumask_size();
+
+	mm_cachep = kmem_cache_create_usercopy("mm_struct",
+			mm_size, ARCH_MIN_MMSTRUCT_ALIGN,
+			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
+			offsetof(struct mm_struct, saved_auxv),
+			sizeof_field(struct mm_struct, saved_auxv),
+			NULL);
+}
+
+void __init proc_caches_init(void)
+{
 	sighand_cachep = kmem_cache_create("sighand_cache",
 			sizeof(struct sighand_struct), 0,
 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_TYPESAFE_BY_RCU|
@@ -3036,19 +3053,6 @@ void __init proc_caches_init(void)
 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
 			NULL);
 
-	/*
-	 * The mm_cpumask is located at the end of mm_struct, and is
-	 * dynamically sized based on the maximum CPU number this system
-	 * can have, taking hotplug into account (nr_cpu_ids).
-	 */
-	mm_size = sizeof(struct mm_struct) + cpumask_size();
-
-	mm_cachep = kmem_cache_create_usercopy("mm_struct",
-			mm_size, ARCH_MIN_MMSTRUCT_ALIGN,
-			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
-			offsetof(struct mm_struct, saved_auxv),
-			sizeof_field(struct mm_struct, saved_auxv),
-			NULL);
 	vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC|SLAB_ACCOUNT);
 	mmap_init();
 	nsproxy_cache_init();