[PATCH] mm/slub: initialize stack depot in boot process

[Hyeonggon Yoo <42.hyeyoo@gmail.com>]

commit ba10d4b46655 ("mm/slub: use stackdepot to save stack trace in
objects") initializes stack depot while creating cache if SLAB_STORE_USER
flag is set.

This can make kernel crash because a cache can be created 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 to at least one cache.

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

Link: https://lkml.org/lkml/2022/2/28/238
Fixes: ba10d4b46655 ("mm/slub: use stackdepot to save stack trace in objects")
Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
---
 include/linux/slab.h |  1 +
 init/main.c          |  1 +
 mm/slab.c            |  4 ++++
 mm/slob.c            |  4 ++++
 mm/slub.c            | 28 +++++++++++++++++++++++++---
 5 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 37bde99b74af..023f3f71ae35 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -139,6 +139,7 @@ struct mem_cgroup;
 /*
  * struct kmem_cache related prototypes
  */
+void __init kmem_cache_init_early(void);
 void __init kmem_cache_init(void);
 bool slab_is_available(void);
 
diff --git a/init/main.c b/init/main.c
index 65fa2e41a9c0..4fdb7975a085 100644
--- a/init/main.c
+++ b/init/main.c
@@ -835,6 +835,7 @@ static void __init mm_init(void)
 	kfence_alloc_pool();
 	report_meminit();
 	stack_depot_early_init();
+	kmem_cache_init_early();
 	mem_init();
 	mem_init_print_info();
 	kmem_cache_init();
diff --git a/mm/slab.c b/mm/slab.c
index ddf5737c63d9..80a6d01aab06 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1196,6 +1196,10 @@ static void __init set_up_node(struct kmem_cache *cachep, int index)
 	}
 }
 
+void __init kmem_cache_init_early(void)
+{
+}
+
 /*
  * Initialisation.  Called after the page allocator have been initialised and
  * before smp_init().
diff --git a/mm/slob.c b/mm/slob.c
index 60c5842215f1..00e323af8be4 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -715,6 +715,10 @@ struct kmem_cache kmem_cache_boot = {
 	.align = ARCH_KMALLOC_MINALIGN,
 };
 
+void __init kmem_cache_init_early(void)
+{
+}
+
 void __init kmem_cache_init(void)
 {
 	kmem_cache = &kmem_cache_boot;
diff --git a/mm/slub.c b/mm/slub.c
index a74afe59a403..40bcd18143b6 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4221,9 +4221,6 @@ 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))
@@ -4810,6 +4807,31 @@ static struct kmem_cache * __init bootstrap(struct kmem_cache *static_cache)
 	return s;
 }
 
+/* Initialize stack depot if needed */
+void __init kmem_cache_init_early(void)
+{
+#ifdef CONFIG_STACKDEPOT
+	slab_flags_t block_flags;
+	char *next_block;
+	char *slab_list;
+
+	if (slub_debug & SLAB_STORE_USER)
+		goto init_stack_depot;
+
+	next_block = slub_debug_string;
+	while (next_block) {
+		next_block = parse_slub_debug_flags(next_block, &block_flags, &slab_list, false);
+		if (block_flags & SLAB_STORE_USER)
+			goto init_stack_depot;
+	}
+
+	return;
+
+init_stack_depot:
+	stack_depot_init();
+#endif
+}
+
 void __init kmem_cache_init(void)
 {
 	static __initdata struct kmem_cache boot_kmem_cache,
-- 
2.33.1