[PATCH] lib/stackdepot: allow optional init and stack_table allocation by kvmalloc()

[Vlastimil Babka]

Currently, enabling CONFIG_STACKDEPOT means its stack_table will be allocated
from memblock, even if stack depot ends up not actually used. The default size
of stack_table is 4MB on 32-bit, 8MB on 64-bit.

This is fine for use-cases such as KASAN which is also a config option and
has overhead on its own. But it's an issue for functionality that has to be
actually enabled on boot (page_owner) or depends on hardware (GPU drivers)
and thus the memory might be wasted. This was raised as an issue when trying
to add stackdepot support for SLUB's debug object tracking functionality. It's
common to build kernels with CONFIG_SLUB_DEBUG and enable slub_debug on boot
only when needed, or create specific kmem caches with debugging for testing
purposes.

It would thus be more efficient if stackdepot's table was allocated only when
actually going to be used. This patch thus makes the allocation (and whole
stack_depot_init() call) optional:

- Add a CONFIG_STACKDEPOT_ALWAYS_INIT flag to keep using the current
  well-defined point of allocation as part of mem_init(). Make CONFIG_KASAN
  select this flag.
- Other users have to call stack_depot_init() as part of their own init when
  it's determined that stack depot will actually be used. This may depend on
  both config and runtime conditions. Convert current users which are
  page_owner and several in the DRM subsystem. Same will be done for SLUB
  later.
- Because the init might now be called after the boot-time memblock allocation
  has given all memory to the buddy allocator, change stack_depot_init() to
  allocate stack_table with kvmalloc() when memblock is no longer available.
  Also handle allocation failure by disabling stackdepot (could have
  theoretically happened even with memblock allocation previously), and don't
  unnecessarily align the memblock allocation to its own size anymore.

[1] https://lore.kernel.org/all/CAMuHMdW=eoVzM1Re5FVoEN87nKfiLmM2+Ah7eNu2KXEhCvbZyA@xxxxxxxxxxxxxx/

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Vijayanand Jitta <vjitta@xxxxxxxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Maxime Ripard <mripard@xxxxxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: David Airlie <airlied@xxxxxxxx>
Cc: Daniel Vetter <daniel@xxxxxxxx>
Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Cc: Oliver Glitta <glittao@xxxxxxxxx>
Cc: Imran Khan <imran.f.khan@xxxxxxxxxx>
---
Hi, I'd appreciate review of the DRM parts - namely that I've got correctly
that stack_depot_init() is called from the proper init functions and iff
stack_depot_save() is going to be used later. Thanks!

 drivers/gpu/drm/drm_dp_mst_topology.c   |  1 +
 drivers/gpu/drm/drm_mm.c                |  4 ++++
 drivers/gpu/drm/i915/intel_runtime_pm.c |  3 +++
 include/linux/stackdepot.h              | 19 ++++++++-------
 init/main.c                             |  3 ++-
 lib/Kconfig                             |  3 +++
 lib/Kconfig.kasan                       |  1 +
 lib/stackdepot.c                        | 32 +++++++++++++++++++++----
 mm/page_owner.c                         |  2 ++
 9 files changed, 53 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 2d1adab9e360..bbe972d59dae 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -5490,6 +5490,7 @@ int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr,
 	mutex_init(&mgr->probe_lock);
 #if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)
 	mutex_init(&mgr->topology_ref_history_lock);
+	stack_depot_init();
 #endif
 	INIT_LIST_HEAD(&mgr->tx_msg_downq);
 	INIT_LIST_HEAD(&mgr->destroy_port_list);
diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
index 7d1c578388d3..8257f9d4f619 100644
--- a/drivers/gpu/drm/drm_mm.c
+++ b/drivers/gpu/drm/drm_mm.c
@@ -980,6 +980,10 @@ void drm_mm_init(struct drm_mm *mm, u64 start, u64 size)
 	add_hole(&mm->head_node);
 
 	mm->scan_active = 0;
+
+#ifdef CONFIG_DRM_DEBUG_MM
+	stack_depot_init();
+#endif
 }
 EXPORT_SYMBOL(drm_mm_init);
 
diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c b/drivers/gpu/drm/i915/intel_runtime_pm.c
index 0d85f3c5c526..806c32ab410b 100644
--- a/drivers/gpu/drm/i915/intel_runtime_pm.c
+++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
@@ -68,6 +68,9 @@ static noinline depot_stack_handle_t __save_depot_stack(void)
 static void init_intel_runtime_pm_wakeref(struct intel_runtime_pm *rpm)
 {
 	spin_lock_init(&rpm->debug.lock);
+
+	if (rpm->available)
+		stack_depot_init();
 }
 
 static noinline depot_stack_handle_t
diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
index c34b55a6e554..60ba99a43745 100644
--- a/include/linux/stackdepot.h
+++ b/include/linux/stackdepot.h
@@ -15,6 +15,16 @@
 
 typedef u32 depot_stack_handle_t;
 
+/*
+ * Every user of stack depot has to call this during its own init when it's
+ * decided that it will be calling stack_depot_save() later.
+ *
+ * The alternative is to select STACKDEPOT_ALWAYS_INIT to have stack depot
+ * enabled as part of mm_init(), for subsystems where it's known at compile time
+ * that stack depot will be used.
+ */
+int stack_depot_init(void);
+
 depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 					unsigned int nr_entries,
 					gfp_t gfp_flags, bool can_alloc);
@@ -30,13 +40,4 @@ int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
 
 void stack_depot_print(depot_stack_handle_t stack);
 
-#ifdef CONFIG_STACKDEPOT
-int stack_depot_init(void);
-#else
-static inline int stack_depot_init(void)
-{
-	return 0;
-}
-#endif	/* CONFIG_STACKDEPOT */
-
 #endif
diff --git a/init/main.c b/init/main.c
index ee4d3e1b3eb9..b6a5833d98f5 100644
--- a/init/main.c
+++ b/init/main.c
@@ -844,7 +844,8 @@ static void __init mm_init(void)
 	init_mem_debugging_and_hardening();
 	kfence_alloc_pool();
 	report_meminit();
-	stack_depot_init();
+	if (IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT))
+		stack_depot_init();
 	mem_init();
 	mem_init_print_info();
 	/* page_owner must be initialized after buddy is ready */
diff --git a/lib/Kconfig b/lib/Kconfig
index 5e7165e6a346..df6bcf0a4cc3 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -671,6 +671,9 @@ config STACKDEPOT
 	bool
 	select STACKTRACE
 
+config STACKDEPOT_ALWAYS_INIT
+	bool
+
 config STACK_HASH_ORDER
 	int "stack depot hash size (12 => 4KB, 20 => 1024KB)"
 	range 12 20
diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index cdc842d090db..695deb603c66 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -39,6 +39,7 @@ menuconfig KASAN
 		   HAVE_ARCH_KASAN_HW_TAGS
 	depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
 	select STACKDEPOT
+	select STACKDEPOT_ALWAYS_INIT
 	help
 	  Enables KASAN (KernelAddressSANitizer) - runtime memory debugger,
 	  designed to find out-of-bounds accesses and use-after-free bugs.
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index b437ae79aca1..a4f449ccd0dc 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -23,6 +23,7 @@
 #include <linux/jhash.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
+#include <linux/mutex.h>
 #include <linux/percpu.h>
 #include <linux/printk.h>
 #include <linux/slab.h>
@@ -145,6 +146,7 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
 #define STACK_HASH_MASK (STACK_HASH_SIZE - 1)
 #define STACK_HASH_SEED 0x9747b28c
 
+DEFINE_MUTEX(stack_depot_init_mutex);
 static bool stack_depot_disable;
 static struct stack_record **stack_table;
 
@@ -161,18 +163,38 @@ static int __init is_stack_depot_disabled(char *str)
 }
 early_param("stack_depot_disable", is_stack_depot_disabled);
 
-int __init stack_depot_init(void)
+/*
+ * __ref because of memblock_alloc(), which will not be actually called after
+ * the __init code is gone
+ */
+__ref int stack_depot_init(void)
 {
-	if (!stack_depot_disable) {
+	mutex_lock(&stack_depot_init_mutex);
+	if (!stack_depot_disable && stack_table == NULL) {
 		size_t size = (STACK_HASH_SIZE * sizeof(struct stack_record *));
 		int i;
 
-		stack_table = memblock_alloc(size, size);
-		for (i = 0; i < STACK_HASH_SIZE;  i++)
-			stack_table[i] = NULL;
+		if (slab_is_available()) {
+			pr_info("Stack Depot allocating hash table with kvmalloc\n");
+			stack_table = kvmalloc(size, GFP_KERNEL);
+		} else {
+			pr_info("Stack Depot allocating hash table with memblock_alloc\n");
+			stack_table = memblock_alloc(size, SMP_CACHE_BYTES);
+		}
+		if (stack_table) {
+			for (i = 0; i < STACK_HASH_SIZE;  i++)
+				stack_table[i] = NULL;
+		} else {
+			pr_err("Stack Depot failed hash table allocationg, disabling\n");
+			stack_depot_disable = true;
+			mutex_unlock(&stack_depot_init_mutex);
+			return -ENOMEM;
+		}
 	}
+	mutex_unlock(&stack_depot_init_mutex);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(stack_depot_init);
 
 /* Calculate hash for a stack */
 static inline u32 hash_stack(unsigned long *entries, unsigned int size)
diff --git a/mm/page_owner.c b/mm/page_owner.c
index a83f546c06b5..a48607b51a97 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -80,6 +80,8 @@ static void init_page_owner(void)
 	if (!page_owner_enabled)
 		return;
 
+	stack_depot_init();
+
 	register_dummy_stack();
 	register_failure_stack();
 	register_early_stack();
-- 
2.33.0