[PATCH v3 3/6] mm/slub: use stackdepot to save stack trace in objects

[Vlastimil Babka]

From: Oliver Glitta <glittao@xxxxxxxxx>

Many stack traces are similar so there are many similar arrays.
Stackdepot saves each unique stack only once.

Replace field addrs in struct track with depot_stack_handle_t handle.  Use
stackdepot to save stack trace.

The benefits are smaller memory overhead and possibility to aggregate
per-cache statistics in the following patch using the stackdepot handle
instead of matching stacks manually.

[ vbabka@xxxxxxx: rebase to 5.17-rc1 and adjust accordingly ]

This was initially merged as commit 788691464c29 and reverted by commit
ae14c63a9f20 due to several issues, that should now be fixed.
The problem of unconditional memory overhead by stackdepot has been
addressed by commit 2dba5eb1c73b ("lib/stackdepot: allow optional init
and stack_table allocation by kvmalloc()"), so the dependency on
stackdepot will result in extra memory usage only when a slab cache
tracking is actually enabled, and not for all CONFIG_SLUB_DEBUG builds.
The build failures on some architectures were also addressed, and the
reported issue with xfs/433 test did not reproduce on 5.17-rc1 with this
patch.

Signed-off-by: Oliver Glitta <glittao@xxxxxxxxx>
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Reviewed-and-tested-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
 init/Kconfig      |  1 +
 lib/Kconfig.debug |  1 +
 mm/slab_common.c  |  5 ++++
 mm/slub.c         | 71 ++++++++++++++++++++++++++---------------------
 4 files changed, 47 insertions(+), 31 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index ddcbefe535e9..adc57f989d87 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1875,6 +1875,7 @@ config SLUB_DEBUG
 	default y
 	bool "Enable SLUB debugging support" if EXPERT
 	depends on SLUB && SYSFS
+	select STACKDEPOT if STACKTRACE_SUPPORT
 	help
 	  SLUB has extensive debug support features. Disabling these can
 	  result in significant savings in code size. This also disables
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 075cd25363ac..78d6139111cd 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -709,6 +709,7 @@ config DEBUG_SLAB
 config SLUB_DEBUG_ON
 	bool "SLUB debugging on by default"
 	depends on SLUB && SLUB_DEBUG
+	select STACKDEPOT_ALWAYS_INIT if STACKTRACE_SUPPORT
 	default n
 	help
 	  Boot with debugging on by default. SLUB boots by default with
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 6ee64d6208b3..73943479a2b7 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -24,6 +24,7 @@
 #include <asm/tlbflush.h>
 #include <asm/page.h>
 #include <linux/memcontrol.h>
+#include <linux/stackdepot.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/kmem.h>
@@ -314,9 +315,13 @@ kmem_cache_create_usercopy(const char *name,
 	 * If no slub_debug was enabled globally, the static key is not yet
 	 * enabled by setup_slub_debug(). Enable it if the cache is being
 	 * created with any of the debugging flags passed explicitly.
+	 * It's also possible that this is the first cache created with
+	 * SLAB_STORE_USER and we should init stack_depot for it.
 	 */
 	if (flags & SLAB_DEBUG_FLAGS)
 		static_branch_enable(&slub_debug_enabled);
+	if (flags & SLAB_STORE_USER)
+		stack_depot_init();
 #endif
 
 	mutex_lock(&slab_mutex);
diff --git a/mm/slub.c b/mm/slub.c
index cd4fd0159911..98c1450c23f0 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -26,6 +26,7 @@
 #include <linux/cpuset.h>
 #include <linux/mempolicy.h>
 #include <linux/ctype.h>
+#include <linux/stackdepot.h>
 #include <linux/debugobjects.h>
 #include <linux/kallsyms.h>
 #include <linux/kfence.h>
@@ -264,8 +265,8 @@ static inline bool kmem_cache_has_cpu_partial(struct kmem_cache *s)
 #define TRACK_ADDRS_COUNT 16
 struct track {
 	unsigned long addr;	/* Called from address */
-#ifdef CONFIG_STACKTRACE
-	unsigned long addrs[TRACK_ADDRS_COUNT];	/* Called from address */
+#ifdef CONFIG_STACKDEPOT
+	depot_stack_handle_t handle;
 #endif
 	int cpu;		/* Was running on cpu */
 	int pid;		/* Pid context */
@@ -724,22 +725,19 @@ static struct track *get_track(struct kmem_cache *s, void *object,
 	return kasan_reset_tag(p + alloc);
 }
 
-static void set_track(struct kmem_cache *s, void *object,
+static void noinline set_track(struct kmem_cache *s, void *object,
 			enum track_item alloc, unsigned long addr)
 {
 	struct track *p = get_track(s, object, alloc);
 
-#ifdef CONFIG_STACKTRACE
+#ifdef CONFIG_STACKDEPOT
+	unsigned long entries[TRACK_ADDRS_COUNT];
 	unsigned int nr_entries;
 
-	metadata_access_enable();
-	nr_entries = stack_trace_save(kasan_reset_tag(p->addrs),
-				      TRACK_ADDRS_COUNT, 3);
-	metadata_access_disable();
-
-	if (nr_entries < TRACK_ADDRS_COUNT)
-		p->addrs[nr_entries] = 0;
+	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 3);
+	p->handle = stack_depot_save(entries, nr_entries, GFP_NOWAIT);
 #endif
+
 	p->addr = addr;
 	p->cpu = smp_processor_id();
 	p->pid = current->pid;
@@ -759,20 +757,19 @@ static void init_tracking(struct kmem_cache *s, void *object)
 
 static void print_track(const char *s, struct track *t, unsigned long pr_time)
 {
+	depot_stack_handle_t handle __maybe_unused;
+
 	if (!t->addr)
 		return;
 
 	pr_err("%s in %pS age=%lu cpu=%u pid=%d\n",
 	       s, (void *)t->addr, pr_time - t->when, t->cpu, t->pid);
-#ifdef CONFIG_STACKTRACE
-	{
-		int i;
-		for (i = 0; i < TRACK_ADDRS_COUNT; i++)
-			if (t->addrs[i])
-				pr_err("\t%pS\n", (void *)t->addrs[i]);
-			else
-				break;
-	}
+#ifdef CONFIG_STACKDEPOT
+	handle = READ_ONCE(t->handle);
+	if (handle)
+		stack_depot_print(handle);
+	else
+		pr_err("object allocation/free stack trace missing\n");
 #endif
 }
 
@@ -1532,6 +1529,8 @@ static int __init setup_slub_debug(char *str)
 			global_slub_debug_changed = true;
 		} else {
 			slab_list_specified = true;
+			if (flags & SLAB_STORE_USER)
+				stack_depot_want_early_init();
 		}
 	}
 
@@ -1549,6 +1548,8 @@ static int __init setup_slub_debug(char *str)
 	}
 out:
 	slub_debug = global_flags;
+	if (slub_debug & SLAB_STORE_USER)
+		stack_depot_want_early_init();
 	if (slub_debug != 0 || slub_debug_string)
 		static_branch_enable(&slub_debug_enabled);
 	else
@@ -4342,18 +4343,26 @@ void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab)
 	objp = fixup_red_left(s, objp);
 	trackp = get_track(s, objp, TRACK_ALLOC);
 	kpp->kp_ret = (void *)trackp->addr;
-#ifdef CONFIG_STACKTRACE
-	for (i = 0; i < KS_ADDRS_COUNT && i < TRACK_ADDRS_COUNT; i++) {
-		kpp->kp_stack[i] = (void *)trackp->addrs[i];
-		if (!kpp->kp_stack[i])
-			break;
-	}
+#ifdef CONFIG_STACKDEPOT
+	{
+		depot_stack_handle_t handle;
+		unsigned long *entries;
+		unsigned int nr_entries;
+
+		handle = READ_ONCE(trackp->handle);
+		if (handle) {
+			nr_entries = stack_depot_fetch(handle, &entries);
+			for (i = 0; i < KS_ADDRS_COUNT && i < nr_entries; i++)
+				kpp->kp_stack[i] = (void *)entries[i];
+		}
 
-	trackp = get_track(s, objp, TRACK_FREE);
-	for (i = 0; i < KS_ADDRS_COUNT && i < TRACK_ADDRS_COUNT; i++) {
-		kpp->kp_free_stack[i] = (void *)trackp->addrs[i];
-		if (!kpp->kp_free_stack[i])
-			break;
+		trackp = get_track(s, objp, TRACK_FREE);
+		handle = READ_ONCE(trackp->handle);
+		if (handle) {
+			nr_entries = stack_depot_fetch(handle, &entries);
+			for (i = 0; i < KS_ADDRS_COUNT && i < nr_entries; i++)
+				kpp->kp_free_stack[i] = (void *)entries[i];
+		}
 	}
 #endif
 #endif
-- 
2.35.1