[Crash-utility] [PATCH] Fix for "kmem <addr>" for kernels configured with CONFIG_SLUB and SLAB_RED_ZONE.

[OGAWA Hirofumi]

If SLAB_RED_ZONE is enabled, slub adds guard zone of sizeof(void *)
onto head of slab page (red zone padding of left of object) on v4.6 or
later.

Without this fix, like following SUPERBLK and [allocate addr] has
difference.

crash> mount
     MOUNT           SUPERBLK     TYPE   DEVNAME   DIRNAME
ffff88013ae58040 ffff88013ac35698 rootfs rootfs    /         
[...]
crash> kmem ffff88013ac35698
CACHE            NAME                 OBJSIZE  ALLOCATED     TOTAL  SLABS  SSIZE
ffff88013ac05bc0 kmalloc-4096            4096        118       126     18    32k
  SLAB              MEMORY            NODE  TOTAL  ALLOCATED  FREE
  ffffea0004eb0c00  ffff88013ac30000     0      7          7     0
  FREE / [ALLOCATED]
  [ffff88013ac35690]
[...]

---

 defs.h    |    1 +
 memory.c  |    8 ++++++++
 symbols.c |    2 ++
 3 files changed, 11 insertions(+)

diff -puN memory.c~slub-red_zone-fix memory.c
--- crash-64/memory.c~slub-red_zone-fix	2017-01-30 10:21:12.123644726 +0900
+++ crash-64-hirofumi/memory.c	2017-01-30 10:21:12.127644748 +0900
@@ -723,6 +723,7 @@ vm_init(void)
 		MEMBER_OFFSET_INIT(kmem_cache_node, "kmem_cache", "node");
 		MEMBER_OFFSET_INIT(kmem_cache_cpu_slab, "kmem_cache", "cpu_slab");
 		MEMBER_OFFSET_INIT(kmem_cache_list, "kmem_cache", "list");
+		MEMBER_OFFSET_INIT(kmem_cache_red_left_pad, "kmem_cache", "red_left_pad");
 		MEMBER_OFFSET_INIT(kmem_cache_name, "kmem_cache", "name");
 		MEMBER_OFFSET_INIT(kmem_cache_flags, "kmem_cache", "flags");
 		MEMBER_OFFSET_INIT(kmem_cache_cpu_freelist, "kmem_cache_cpu", "freelist");
@@ -18442,6 +18443,13 @@ do_slab_slub(struct meminfo *si, int ver
 			fprintf(fp, "< SLUB: free list END (%d found) >\n", i);
 	}
 
+	if (VALID_MEMBER(kmem_cache_red_left_pad)) {
+#define SLAB_RED_ZONE 0x00000400UL
+		ulong flags = ULONG(si->cache_buf + OFFSET(kmem_cache_flags));
+		ulong red_left_pad = ULONG(si->cache_buf + OFFSET(kmem_cache_red_left_pad));
+		if (flags & SLAB_RED_ZONE)
+			vaddr += red_left_pad;
+	}
 	for (p = vaddr; p < vaddr + objects * si->size; p += si->size) {
 		hq_open();
 		is_free = FALSE;
diff -puN defs.h~slub-red_zone-fix defs.h
--- crash-64/defs.h~slub-red_zone-fix	2017-01-30 10:21:12.124644731 +0900
+++ crash-64-hirofumi/defs.h	2017-02-01 00:11:33.445552457 +0900
@@ -1696,6 +1696,7 @@ struct offset_table {
 	long kmem_cache_align;
 	long kmem_cache_name;
 	long kmem_cache_list;
+	long kmem_cache_red_left_pad;
 	long kmem_cache_node;
 	long kmem_cache_cpu_slab;
 	long page_inuse;
diff -puN symbols.c~slub-red_zone-fix symbols.c
--- crash-64/symbols.c~slub-red_zone-fix	2017-01-30 10:21:12.124644731 +0900
+++ crash-64-hirofumi/symbols.c	2017-02-01 00:11:33.446552463 +0900
@@ -9330,6 +9330,8 @@ dump_offset_table(char *spec, ulong make
                 OFFSET(kmem_cache_name));
         fprintf(fp, "               kmem_cache_list: %ld\n",
                 OFFSET(kmem_cache_list));
+        fprintf(fp, "       kmem_cache_red_left_pad: %ld\n",
+                OFFSET(kmem_cache_red_left_pad));
         fprintf(fp, "               kmem_cache_node: %ld\n",
                 OFFSET(kmem_cache_node));
         fprintf(fp, "           kmem_cache_cpu_slab: %ld\n",
_

-- 
OGAWA Hirofumi <hirofumi at mail.parknet.co.jp>