Revert "mm/slub: use stackdepot to save stack trace in objects"

This reverts commit 7886914.

It's not clear why, but it causes unexplained problems in entirely
unrelated xfs code.  The most likely explanation is some slab
corruption, possibly triggered due to CONFIG_SLUB_DEBUG_ON.  See [1].

It ends up having a few other problems too, like build errors on
arch/arc, and Geert reporting it using much more memory on m68k [3] (it
probably does so elsewhere too, but it is probably just more noticeable
on m68k).

The architecture issues (both build and memory use) are likely just
because this change effectively force-enabled STACKDEPOT (along with a
very bad default value for the stackdepot hash size).  But together with
the xfs issue, this all smells like "this commit was not ready" to me.

Link: https://lore.kernel.org/linux-xfs/YPE3l82acwgI2OiV@infradead.org/ [1]
Link: https://lore.kernel.org/lkml/202107150600.LkGNb4Vb-lkp@intel.com/ [2]
Link: https://lore.kernel.org/lkml/CAMuHMdW=eoVzM1Re5FVoEN87nKfiLmM2+Ah7eNu2KXEhCvbZyA@mail.gmail.com/ [3]
Reported-by: Christoph Hellwig <hch@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: torvalds

init/Kconfig

@@ -1847,7 +1847,6 @@ 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

mm/slub.c

@@ -26,7 +26,6 @@
 #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>
@@ -207,8 +206,8 @@ 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_STACKDEPOT
-	depot_stack_handle_t handle;
+#ifdef CONFIG_STACKTRACE
+	unsigned long addrs[TRACK_ADDRS_COUNT];	/* Called from address */
 #endif
 	int cpu;		/* Was running on cpu */
 	int pid;		/* Pid context */
@@ -612,27 +611,22 @@ static struct track *get_track(struct kmem_cache *s, void *object,
 	return kasan_reset_tag(p + alloc);
 }
 
-#ifdef CONFIG_STACKDEPOT
-static depot_stack_handle_t save_stack_depot_trace(gfp_t flags)
-{
-	unsigned long entries[TRACK_ADDRS_COUNT];
-	depot_stack_handle_t handle;
-	unsigned int nr_entries;
-
-	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 4);
-	handle = stack_depot_save(entries, nr_entries, flags);
-	return handle;
-}
-#endif
-
 static void set_track(struct kmem_cache *s, void *object,
 			enum track_item alloc, unsigned long addr)
 {
 	struct track *p = get_track(s, object, alloc);
 
 	if (addr) {
-#ifdef CONFIG_STACKDEPOT
-		p->handle = save_stack_depot_trace(GFP_NOWAIT);
+#ifdef CONFIG_STACKTRACE
+		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;
 #endif
 		p->addr = addr;
 		p->cpu = smp_processor_id();
@@ -659,19 +653,14 @@ static void print_track(const char *s, struct track *t, unsigned long pr_time)
 
 	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_STACKDEPOT
+#ifdef CONFIG_STACKTRACE
 	{
-		depot_stack_handle_t handle;
-		unsigned long *entries;
-		unsigned int nr_entries;
-
-		handle = READ_ONCE(t->handle);
-		if (!handle) {
-			pr_err("object allocation/free stack trace missing\n");
-		} else {
-			nr_entries = stack_depot_fetch(handle, &entries);
-			stack_trace_print(entries, nr_entries, 0);
-		}
+		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;
 	}
 #endif
 }
@@ -4045,26 +4034,18 @@ void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
 	objp = fixup_red_left(s, objp);
 	trackp = get_track(s, objp, TRACK_ALLOC);
 	kpp->kp_ret = (void *)trackp->addr;
-#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];
-		}
+#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;
+	}
 
-		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];
-		}
+	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;
 	}
 #endif
 #endif