[PATCH tip/core/rcu 1/2] mm/slub: Fix backtrace of objects to handle redzone adjustment

[Paul E. McKenney]

From: Maninder Singh <maninder1.s@xxxxxxxxxxx>

This commit fixes commit 8e7f37f2aaa5 ("mm: Add mem_dump_obj() to print
source of memory block").

With current code, the backtrace of allocated object is incorrect:
/ # cat /proc/meminfo
[   14.969843]  slab kmalloc-64 start c8ab0140 data offset 64 pointer offset 0 size 64 allocated at 0x6b6b6b6b
[   14.970635]     0x6b6b6b6b
[   14.970794]     0x6b6b6b6b
[   14.970932]     0x6b6b6b6b
[   14.971077]     0x6b6b6b6b
[   14.971202]     0x6b6b6b6b
[   14.971317]     0x6b6b6b6b
[   14.971423]     0x6b6b6b6b
[   14.971635]     0x6b6b6b6b
[   14.971740]     0x6b6b6b6b
[   14.971871]     0x6b6b6b6b
[   14.972229]     0x6b6b6b6b
[   14.972363]     0x6b6b6b6b
[   14.972505]     0xa56b6b6b
[   14.972631]     0xbbbbbbbb
[   14.972734]     0xc8ab0400
[   14.972891]     meminfo_proc_show+0x40/0x4fc

The reason is that the object address was not adjusted for the red zone.
With this fix, the backtrace is correct:
/ # cat /proc/meminfo
[   14.870782]  slab kmalloc-64 start c8ab0140 data offset 64 pointer offset 128 size 64 allocated at meminfo_proc_show+0x40/0x4f4
[   14.871817]     meminfo_proc_show+0x40/0x4f4
[   14.872035]     seq_read_iter+0x18c/0x4c4
[   14.872229]     proc_reg_read_iter+0x84/0xac
[   14.872433]     generic_file_splice_read+0xe8/0x17c
[   14.872621]     splice_direct_to_actor+0xb8/0x290
[   14.872747]     do_splice_direct+0xa0/0xe0
[   14.872896]     do_sendfile+0x2d0/0x438
[   14.873044]     sys_sendfile64+0x12c/0x140
[   14.873229]     ret_fast_syscall+0x0/0x58
[   14.873372]     0xbe861de4

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Vaneet Narang <v.narang@xxxxxxxxxxx>
Signed-off-by: Maninder Singh <maninder1.s@xxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 mm/slub.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/slub.c b/mm/slub.c
index feda53ae62ba..8f2d13508ec9 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4002,6 +4002,7 @@ void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
 	    !(s->flags & SLAB_STORE_USER))
 		return;
 #ifdef CONFIG_SLUB_DEBUG
+	objp = fixup_red_left(s, objp);
 	trackp = get_track(s, objp, TRACK_ALLOC);
 	kpp->kp_ret = (void *)trackp->addr;
 #ifdef CONFIG_STACKTRACE
-- 
2.31.1.189.g2e36527f23