mm/slub: Add Support for free path information of an object

This commit adds enables a stack dump for the last free of an object:

slab kmalloc-64 start c8ab0140 data offset 64 pointer offset 0 size 64 allocated at meminfo_proc_show+0x40/0x4fc
[   20.192078]     meminfo_proc_show+0x40/0x4fc
[   20.192263]     seq_read_iter+0x18c/0x4c4
[   20.192430]     proc_reg_read_iter+0x84/0xac
[   20.192617]     generic_file_splice_read+0xe8/0x17c
[   20.192816]     splice_direct_to_actor+0xb8/0x290
[   20.193008]     do_splice_direct+0xa0/0xe0
[   20.193185]     do_sendfile+0x2d0/0x438
[   20.193345]     sys_sendfile64+0x12c/0x140
[   20.193523]     ret_fast_syscall+0x0/0x58
[   20.193695]     0xbeeacde4
[   20.193822]  Free path:
[   20.193935]     meminfo_proc_show+0x5c/0x4fc
[   20.194115]     seq_read_iter+0x18c/0x4c4
[   20.194285]     proc_reg_read_iter+0x84/0xac
[   20.194475]     generic_file_splice_read+0xe8/0x17c
[   20.194685]     splice_direct_to_actor+0xb8/0x290
[   20.194870]     do_splice_direct+0xa0/0xe0
[   20.195014]     do_sendfile+0x2d0/0x438
[   20.195174]     sys_sendfile64+0x12c/0x140
[   20.195336]     ret_fast_syscall+0x0/0x58
[   20.195491]     0xbeeacde4

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Co-developed-by: Vaneet Narang <v.narang@samsung.com>
Signed-off-by: Vaneet Narang <v.narang@samsung.com>
Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Author: maninder42

mm/slab.h

@@ -640,6 +640,7 @@ struct kmem_obj_info {
 	struct kmem_cache *kp_slab_cache;
 	void *kp_ret;
 	void *kp_stack[KS_ADDRS_COUNT];
+	void *kp_free_stack[KS_ADDRS_COUNT];
 };
 void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page);
 #endif

mm/slab_common.c

@@ -564,7 +564,7 @@ EXPORT_SYMBOL_GPL(kmem_valid_obj);
  * depends on the type of object and on how much debugging is enabled.
  * For a slab-cache object, the fact that it is a slab object is printed,
  * and, if available, the slab name, return address, and stack trace from
- * the allocation of that object.
+ * the allocation and last free path of that object.
  *
  * This function will splat if passed a pointer to a non-slab object.
  * If you are not sure what type of object you have, you should instead
@@ -609,6 +609,16 @@ void kmem_dump_obj(void *object)
 			break;
 		pr_info("    %pS\n", kp.kp_stack[i]);
 	}
+
+	if (kp.kp_free_stack[0])
+		pr_cont(" Free path:\n");
+
+	for (i = 0; i < ARRAY_SIZE(kp.kp_free_stack); i++) {
+		if (!kp.kp_free_stack[i])
+			break;
+		pr_info("    %pS\n", kp.kp_free_stack[i]);
+	}
+
 }
 EXPORT_SYMBOL_GPL(kmem_dump_obj);
 #endif

mm/slub.c

@@ -4011,6 +4011,13 @@ void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
 		if (!kpp->kp_stack[i])
 			break;
 	}
+
+	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
 }

mm/util.c

@@ -983,7 +983,7 @@ int __weak memcmp_pages(struct page *page1, struct page *page2)
  * depends on the type of object and on how much debugging is enabled.
  * For example, for a slab-cache object, the slab name is printed, and,
  * if available, the return address and stack trace from the allocation
- * of that object.
+ * and last free path of that object.
  */
 void mem_dump_obj(void *object)
 {