On Tue, Mar 16, 2021 at 04:07:10PM +0530, Maninder Singh wrote:
> fixing commit 8e7f37f2aaa5 ("mm: Add mem_dump_obj() to print source
> of memory block")
>
> with current code, Backtrace of allocated object is coming wrong:
> / # 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
>
> And reason is red zone was not adjusted from object address.
> after adding fixup for redzone, backtrace is coming 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
>
> Signed-off-by: Vaneet Narang <v.narang@xxxxxxxxxxx>
> Signed-off-by: Maninder Singh <maninder1.s@xxxxxxxxxxx>
Good catch, thank you! For the series:
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
On the other hand, if you would like me to take these, we need to get
a maintainer ack.
Thanx, Paul
> ---
> mm/slub.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 1912c4614248..9d13f0117ae6 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4052,6 +4052,7 @@ 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
> --
> 2.17.1
>
