[PATCH/RFC] debugobjects/slub: Print slab info and backtrace.
From: greearb
Date: Thu Nov 02 2023 - 21:48:09 EST
From: Ben Greear <greearb@xxxxxxxxxxxxxxx>
When debugobjects detects a problem, it may be in generic code
where the backtraces currently printed are not helpful.
To try to improve this, store the backtrace of where the
debug_obj was created and print that out when problems
are found.
Also print out slub info for the object held by the
debug_obj. In my particular case, this was not super
useful, appearantly because of all of the KASAN and other
debugging I have enabled. Still, might provide a few
clues.
Signed-off-by: Ben Greear <greearb@xxxxxxxxxxxxxxx>
---
include/linux/debugobjects.h | 5 +++++
include/linux/slab.h | 11 +++++++++++
include/linux/slab_def.h | 2 ++
lib/debugobjects.c | 37 ++++++++++++++++++++++++++++++++++++
mm/slab.h | 4 ++--
mm/slub.c | 34 +++++++++++++++++++++++++++++----
6 files changed, 87 insertions(+), 6 deletions(-)
diff --git a/include/linux/debugobjects.h b/include/linux/debugobjects.h
index 32444686b6ff..8e8df719bd88 100644
--- a/include/linux/debugobjects.h
+++ b/include/linux/debugobjects.h
@@ -31,6 +31,11 @@ struct debug_obj {
unsigned int astate;
void *object;
const struct debug_obj_descr *descr;
+#ifdef CONFIG_STACKDEPOT
+#define DEBUG_OBJ_ADDRS_COUNT 16
+ /* Including stackdepot.h blows up the build, so open-code the handle. */
+ u64 trace_handle;
+#endif
};
/**
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 8228d1276a2f..87a5da669eaf 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -793,4 +793,15 @@ int slab_dead_cpu(unsigned int cpu);
#define slab_dead_cpu NULL
#endif
+
+/**
+ * Calling this on allocated memory will print debugging info
+ * about the object, if CONFIG_SLAB_DEBUG is enabled.
+ */
+#ifdef CONFIG_SLUB_DEBUG
+void slab_print_mem_info(const void *x);
+#else
+static inline void slab_print_mem_info(const void *x) { }
+#endif
+
#endif /* _LINUX_SLAB_H */
diff --git a/include/linux/slab_def.h b/include/linux/slab_def.h
index a61e7d55d0d3..db3ce19be339 100644
--- a/include/linux/slab_def.h
+++ b/include/linux/slab_def.h
@@ -121,4 +121,6 @@ static inline int objs_per_slab(const struct kmem_cache *cache,
return cache->num;
}
+static inline void slab_print_mem_info(const void *x) { }
+
#endif /* _LINUX_SLAB_DEF_H */
diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index a517256a270b..1f458e473bc5 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -17,6 +17,8 @@
#include <linux/hash.h>
#include <linux/kmemleak.h>
#include <linux/cpu.h>
+#include <linux/slab.h>
+#include <linux/stackdepot.h>
#define ODEBUG_HASH_BITS 14
#define ODEBUG_HASH_SIZE (1 << ODEBUG_HASH_BITS)
@@ -216,6 +218,33 @@ static struct debug_obj *__alloc_object(struct hlist_head *list)
return obj;
}
+#ifdef CONFIG_STACKDEPOT
+static void debug_print_stack_info(struct debug_obj *object)
+{
+ if (object->trace_handle) {
+ pr_err("debugobjects: debug_obj allocated at:\n");
+ stack_depot_print(object->trace_handle);
+ pr_err("end of stack dump\n");
+ }
+}
+
+static noinline depot_stack_handle_t set_track_prepare(void)
+{
+ depot_stack_handle_t trace_handle;
+ unsigned long entries[DEBUG_OBJ_ADDRS_COUNT];
+ unsigned int nr_entries;
+
+ nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 3);
+ trace_handle = stack_depot_save(entries, nr_entries, GFP_NOWAIT);
+
+ return trace_handle;
+}
+
+#else
+static void debug_print_stack_info(struct debug_obj *object) { }
+static depot_stack_handle_t set_track_prepare(void) { }
+#endif
+
static struct debug_obj *
alloc_object(void *addr, struct debug_bucket *b, const struct debug_obj_descr *descr)
{
@@ -272,6 +301,12 @@ alloc_object(void *addr, struct debug_bucket *b, const struct debug_obj_descr *d
obj->state = ODEBUG_STATE_NONE;
obj->astate = 0;
hlist_add_head(&obj->node, &b->list);
+
+ /* Save stack of where object was created */
+#ifdef CONFIG_STACKDEPOT
+ /* kernel backtrace */
+ obj->trace_handle = set_track_prepare();
+#endif
}
return obj;
}
@@ -515,6 +550,8 @@ static void debug_print_object(struct debug_obj *obj, char *msg)
"object: %p object type: %s hint: %pS\n",
msg, obj_states[obj->state], obj->astate,
obj->object, descr->name, hint);
+ debug_print_stack_info(obj);
+ slab_print_mem_info(obj->object);
}
debug_objects_warnings++;
}
diff --git a/mm/slab.h b/mm/slab.h
index 799a315695c6..d977c093e90d 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -399,14 +399,14 @@ DECLARE_STATIC_KEY_TRUE(slub_debug_enabled);
#else
DECLARE_STATIC_KEY_FALSE(slub_debug_enabled);
#endif
-extern void print_tracking(struct kmem_cache *s, void *object);
+extern void print_tracking(struct kmem_cache *s, const void *object);
long validate_slab_cache(struct kmem_cache *s);
static inline bool __slub_debug_enabled(void)
{
return static_branch_unlikely(&slub_debug_enabled);
}
#else
-static inline void print_tracking(struct kmem_cache *s, void *object)
+static inline void print_tracking(struct kmem_cache *s, const void *object)
{
}
static inline bool __slub_debug_enabled(void)
diff --git a/mm/slub.c b/mm/slub.c
index f7940048138c..7d0c648369ab 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -760,10 +760,10 @@ static inline unsigned int get_info_end(struct kmem_cache *s)
return s->inuse;
}
-static struct track *get_track(struct kmem_cache *s, void *object,
+static struct track *get_track(struct kmem_cache *s, const void *object,
enum track_item alloc)
{
- struct track *p;
+ const struct track *p;
p = object + get_info_end(s);
@@ -841,11 +841,14 @@ static void print_track(const char *s, struct track *t, unsigned long pr_time)
#endif
}
-void print_tracking(struct kmem_cache *s, void *object)
+void print_tracking(struct kmem_cache *s, const void *object)
{
unsigned long pr_time = jiffies;
- if (!(s->flags & SLAB_STORE_USER))
+ if (!(s->flags & SLAB_STORE_USER)) {
+ pr_err("slub-print-tracking, STORE-USER not enabled, cache: %s flags: 0x%x\n",
+ s->name, s->flags);
return;
+ }
print_track("Allocated", get_track(s, object, TRACK_ALLOC), pr_time);
print_track("Freed", get_track(s, object, TRACK_FREE), pr_time);
@@ -1712,6 +1715,29 @@ slab_flags_t kmem_cache_flags(unsigned int object_size,
return flags | slub_debug_local;
}
+
+void slab_print_mem_info(const void *x)
+{
+ struct slab *slab;
+
+ if (unlikely(ZERO_OR_NULL_PTR(x)))
+ return;
+
+ slab = virt_to_slab(x);
+ if (!slab) {
+ pr_err("slub-print-mem-info, could not find slab for virt addr: %p\n",
+ x);
+ return;
+ }
+
+ pr_err("slab-info, slab: %p\n", slab);
+ print_slab_info(slab);
+ pr_err("slab-tracking-info: cache: %s (%p)\n",
+ slab->slab_cache->name, slab->slab_cache);
+ print_tracking(slab->slab_cache, x);
+ pr_err("end of slab-tracking-info\n");
+}
+
#else /* !CONFIG_SLUB_DEBUG */
static inline void setup_object_debug(struct kmem_cache *s, void *object) {}
static inline
--
2.41.0