mm/slub: initialize stack depot in boot process

commit ba10d4b ("mm/slub: use stackdepot to save stack trace in
objects") initializes stack depot in cache creation if SLAB_STORE_USER
flag is set.

This can make kernel crash because a cache can be crashed in various
contexts. For example if user sets slub_debug=U, kernel crashes
because create_boot_cache() calls stack_depot_init(), which tries to
allocate hash table using memblock_alloc() if slab is not available.
But memblock is also not available at that time.

This patch solves the problem by initializing stack depot early
in boot process if SLAB_STORE_USER debug flag is set globally
or the flag is set for at least one cache.

[ elver@google.com: initialize stack depot depending on slub_debug
  parameter instead of allowing stack_depot_init() to be called
  during kmem_cache_init() for simplicity. ]

[ vbabka@suse.cz: parse slub_debug parameter in setup_slub_debug()
  and initialize stack depot in stack_depot_early_init(). ]

Link: https://lore.kernel.org/all/YhyeaP8lrzKgKm5A@ip-172-31-19-208.ap-northeast-1.compute.internal/
Fixes: ba10d4b ("mm/slub: use stackdepot to save stack trace in objects")
Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>

include/linux/slab.h

@@ -763,6 +763,12 @@ extern void kvfree_sensitive(const void *addr, size_t len);
 unsigned int kmem_cache_size(struct kmem_cache *s);
 void __init kmem_cache_init_late(void);
 
+#if defined(CONFIG_SLUB_DEBUG) && defined(CONFIG_STACKDEPOT)
+int slab_stack_depot_init(void);
+#else
+int slab_stack_depot_init(void) { return 0; }
+#endif
+
 #if defined(CONFIG_SMP) && defined(CONFIG_SLAB)
 int slab_prepare_cpu(unsigned int cpu);
 int slab_dead_cpu(unsigned int cpu);

include/linux/stackdepot.h

@@ -12,6 +12,7 @@
 #define _LINUX_STACKDEPOT_H
 
 #include <linux/gfp.h>
+#include <linux/slab.h>
 
 typedef u32 depot_stack_handle_t;
 
@@ -32,7 +33,7 @@ int stack_depot_init(void);
 #ifdef CONFIG_STACKDEPOT_ALWAYS_INIT
 static inline int stack_depot_early_init(void)	{ return stack_depot_init(); }
 #else
-static inline int stack_depot_early_init(void)	{ return 0; }
+static inline int stack_depot_early_init(void)	{ return slab_stack_depot_init(); }
 #endif
 
 depot_stack_handle_t stack_depot_save(unsigned long *entries,

mm/slub.c

@@ -646,6 +646,14 @@ static slab_flags_t slub_debug;
 
 static char *slub_debug_string;
 static int disable_higher_order_debug;
+static bool init_stack_depot;
+
+int slab_stack_depot_init(void)
+{
+	if (init_stack_depot)
+		stack_depot_init();
+	return 0;
+}
 
 /*
  * slub is about to manipulate internal object metadata.  This memory lies
@@ -1531,6 +1539,8 @@ static int __init setup_slub_debug(char *str)
 			global_slub_debug_changed = true;
 		} else {
 			slab_list_specified = true;
+			if (flags & SLAB_STORE_USER)
+				init_stack_depot = true;
 		}
 	}
 
@@ -1546,6 +1556,10 @@ static int __init setup_slub_debug(char *str)
 			global_flags = slub_debug;
 		slub_debug_string = saved_str;
 	}
+
+	if (global_flags & SLAB_STORE_USER)
+		init_stack_depot = true;
+
 out:
 	slub_debug = global_flags;
 	if (slub_debug != 0 || slub_debug_string)
@@ -1556,6 +1570,7 @@ static int __init setup_slub_debug(char *str)
 	     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;
 }
 
@@ -4221,9 +4236,6 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
 	s->remote_node_defrag_ratio = 1000;
 #endif
 
-	if (s->flags & SLAB_STORE_USER && IS_ENABLED(CONFIG_STACKDEPOT))
-		stack_depot_init();
-
 	/* Initialize the pre-computed randomized freelist if slab is up */
 	if (slab_state >= UP) {
 		if (init_cache_random_seq(s))