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Subject[PATCH v2] mm/slub: initialize stack depot in boot process
commit ba10d4b46655 ("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: ba10d4b46655 ("mm/slub: use stackdepot to save stack trace in objects")
Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
---
include/linux/slab.h | 6 ++++++
include/linux/stackdepot.h | 3 ++-
mm/slub.c | 18 +++++++++++++++---
3 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 37bde99b74af..062128e0db10 100644
--- a/include/linux/slab.h
+++ b/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);
diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
index 17f992fe6355..a813a2673c48 100644
--- a/include/linux/stackdepot.h
+++ b/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,
diff --git a/mm/slub.c b/mm/slub.c
index a74afe59a403..2419fc3cc9f3 100644
--- a/mm/slub.c
+++ b/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))
--
2.33.1
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