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Subject[RFC PATCH] mm: slub: print kernel addresses when CONFIG_SLUB_DEBUG=y
Date
From: Miles Chen <miles.chen@mediatek.com>

This RFC patch is sent to discuss the printing address with %p issue.

Since commit ad67b74d2469d9b8 ("printk: hash addresses printed with %p"),
%p gives obfuscated addresses now. When CONFIG_SLUB_DEBUG=y, it is still
useful to get real virtual addresses.

Possible approaches are:
1. stop printing kernel addresses
2. print kernel addresses with %pK,
3. print kernel addresses with %px.
4. do nothing

This patch takes %px approach and shows the output here.
(%px will causes checkpatch warnings, let us ignore the warning here to
have the discussion). Also, use DUMP_PREFIX_OFFSET instead of
DUMP_PREFIX_ADDRESS.

Before this patch:

INFO: Slab 0x(____ptrval____) objects=25 used=10 fp=0x(____ptrval____)
INFO: Object 0x(____ptrval____) @offset=1408 fp=0x(____ptrval____)
Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5
Redzone (____ptrval____): bb bb bb bb bb bb bb bb
Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
...
FIX kmalloc-128: Object at 0x(____ptrval____) not freed

After this patch:

INFO: Slab 0xffffffbf00f57000 objects=25 used=23 fp=0xffffffc03d5c3500
INFO: Object 0xffffffc03d5c3500 @offset=13568 fp=0xffffffc03d5c0800
Redzone 00000000: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Redzone 00000010: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Redzone 00000020: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Redzone 00000030: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Redzone 00000040: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Redzone 00000050: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Redzone 00000060: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Redzone 00000070: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
Object 00000000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Object 00000010: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Object 00000020: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Object 00000030: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Object 00000040: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Object 00000050: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Object 00000060: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
Object 00000070: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5
Redzone 00000000: bb bb bb bb bb bb bb bb
Padding 00000000: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
Padding 00000010: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
Padding 00000020: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
Padding 00000030: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
...
FIX kmalloc-128: Object at 0xffffffc03d5c3500 not freed

Signed-off-by: Miles Chen <miles.chen@mediatek.com>
---
mm/slub.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 8834563cdb4b..bc1fb8e81557 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -528,7 +528,7 @@ static void print_section(char *level, char *text, u8 *addr,
unsigned int length)
{
metadata_access_enable();
- print_hex_dump(level, text, DUMP_PREFIX_ADDRESS, 16, 1, addr,
+ print_hex_dump(level, text, DUMP_PREFIX_OFFSET, 16, 1, addr,
length, 1);
metadata_access_disable();
}
@@ -611,7 +611,7 @@ static void print_tracking(struct kmem_cache *s, void *object)

static void print_page_info(struct page *page)
{
- pr_err("INFO: Slab 0x%p objects=%u used=%u fp=0x%p flags=0x%04lx\n",
+ pr_err("INFO: Slab 0x%px objects=%u used=%u fp=0x%px flags=0x%04lx\n",
page, page->objects, page->inuse, page->freelist, page->flags);

}
@@ -653,7 +653,7 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)

print_page_info(page);

- pr_err("INFO: Object 0x%p @offset=%tu fp=0x%p\n\n",
+ pr_err("INFO: Object 0x%px @offset=%tu fp=0x%px\n\n",
p, p - addr, get_freepointer(s, p));

if (s->flags & SLAB_RED_ZONE)
@@ -991,7 +991,7 @@ static void trace(struct kmem_cache *s, struct page *page, void *object,
int alloc)
{
if (s->flags & SLAB_TRACE) {
- pr_info("TRACE %s %s 0x%p inuse=%d fp=0x%p\n",
+ pr_info("TRACE %s %s 0x%px inuse=%d fp=0x%p\n",
s->name,
alloc ? "alloc" : "free",
object, page->inuse,
@@ -1212,7 +1212,7 @@ static noinline int free_debug_processing(
slab_unlock(page);
spin_unlock_irqrestore(&n->list_lock, flags);
if (!ret)
- slab_fix(s, "Object at 0x%p not freed", object);
+ slab_fix(s, "Object at 0x%px not freed", object);
return ret;
}

@@ -3693,7 +3693,7 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
for_each_object(p, s, addr, page->objects) {

if (!test_bit(slab_index(p, s, addr), map)) {
- pr_err("INFO: Object 0x%p @offset=%tu\n", p, p - addr);
+ pr_err("INFO: Object 0x%px @offset=%tu\n", p, p - addr);
print_tracking(s, p);
}
}
--
2.18.0
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