Re: [BISECTED] BUG: Regression: A Problem with /sys/kernel/debug/kmemleak output: backtrace not printed since 6.2.0-rc1

Mirsad Todorovac
2023-01-12T19:47:47Z

On 1/4/23 17:08, Mirsad Goran Todorovac wrote:

> I hate to bring bad news again, but there seems to be a problem with the output of /sys/kernel/debug/kmemleak:
>
> [root@pc-mtodorov ~]# cat /sys/kernel/debug/kmemleak
> unreferenced object 0xffff951c118568b0 (size 16):
>   comm "kworker/u12:2", pid 56, jiffies 4294893952 (age 4356.548s)
>   hex dump (first 16 bytes):
>     6d 65 6d 73 74 69 63 6b 30 00 00 00 00 00 00 00 memstick0.......
>   backtrace:
> [root@pc-mtodorov ~]#
>
> Apparently, backtrace of called functions on the stack is no longer printed with the list of memory leaks.
>
> This appeared on Lenovo desktop 10TX000VCR, with AlmaLinux 8.7 and BIOS version M22KT49A (11/10/2022)
> and 6.2-rc1 and 6.2-rc2 builds.
>
> This worked on 6.1 with the same CONFIG_KMEMLEAK=y and MGLRU enabled on a vanilla mainstream kernel
> from Mr. Torvalds' tree. I don't know if this is deliberate feature for some reason or a bug.
>
> Please find attached the config, lshw and kmemleak output.

Hi all,

The bisection gave this commit as the culprit for the severed stack backtrace print
in /sys/kernel/debug/kmemleak:

mtodorov@domac:~/linux/kernel/linux_torvalds$ git bisect good
56a61617dd2276cbc56a6c868599716386d70041 is the first bad commit
commit 56a61617dd2276cbc56a6c868599716386d70041
Author: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
Date: Thu Oct 27 17:50:24 2022 +0800

mm: use stack_depot for recording kmemleak's backtrace

Using stack_depot to record kmemleak's backtrace which has been
implemented on slub for reducing redundant information.

The complete bisect log is:

mtodorov@domac:~/linux/kernel/linux_torvalds$ git bisect log
git bisect start '--' 'mm'
# good: [830b3c68c1fb1e9176028d02ef86f3cf76aa2476] Linux 6.1
git bisect good 830b3c68c1fb1e9176028d02ef86f3cf76aa2476
# bad: [1b929c02afd37871d5afb9d498426f83432e71c2] Linux 6.2-rc1
git bisect bad 1b929c02afd37871d5afb9d498426f83432e71c2
# good: [8b9ed79c2d587bec5f603d66801478a5af9af842] Merge tag 'x86_asm_for_v6.2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
git bisect good 8b9ed79c2d587bec5f603d66801478a5af9af842
# good: [e83b39d6bbdb6d25bd6f5c258832774635d29b47] mm: make drop_caches keep reclaiming on all nodes
git bisect good e83b39d6bbdb6d25bd6f5c258832774635d29b47
# good: [9997bc017549acd6425e32300eff28424ffeeb6b] zsmalloc: implement writeback mechanism for zsmalloc
git bisect good 9997bc017549acd6425e32300eff28424ffeeb6b
# good: [6287b7dae80944bfa37784a8f9d6861a4facaa6e] mm,thp,rmap: fix races between updates of subpages_mapcount
git bisect good 6287b7dae80944bfa37784a8f9d6861a4facaa6e
# good: [8fa590bf344816c925810331eea8387627bbeb40] Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm
git bisect good 8fa590bf344816c925810331eea8387627bbeb40
# good: [4f292c4de4f6fb83776c0ff22674121eb6ddfa2f] Merge tag 'x86_mm_for_6.2_v2' of
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
git bisect good 4f292c4de4f6fb83776c0ff22674121eb6ddfa2f
# bad: [1ea9d333ba475041efe43d9d9bc32e64aea2ea2b] Merge tag 'mm-stable-2022-12-17-2' of
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
git bisect bad 1ea9d333ba475041efe43d9d9bc32e64aea2ea2b
# bad: [56a61617dd2276cbc56a6c868599716386d70041] mm: use stack_depot for recording kmemleak's backtrace
git bisect bad 56a61617dd2276cbc56a6c868599716386d70041
# good: [61b963b52f59524e27692bc1c14bfb2459e32eb3] mm/gup_test: free memory allocated via kvcalloc() using kvfree()
git bisect good 61b963b52f59524e27692bc1c14bfb2459e32eb3
# first bad commit: [56a61617dd2276cbc56a6c868599716386d70041] mm: use stack_depot for recording kmemleak's backtrace
# good: [9102b78b6f6ae6af3557114c265c266b312c1319] maple_tree: update copyright dates for test code
git bisect good 9102b78b6f6ae6af3557114c265c266b312c1319
# first bad commit: [56a61617dd2276cbc56a6c868599716386d70041] mm: use stack_depot for recording kmemleak's backtrace
You have mail in /var/mail/mtodorov
mtodorov@domac:~/linux/kernel/linux_torvalds$

The platform is 10TX000VCR (LENOVO_MT_10TX_BU_Lenovo_FM_V530S-07ICB) running AlmaLinux 8.7
(CentOS clone) and BIOS M22KT49A.

GCC used was:

mtodorov@domac:~/linux/kernel/linux_torvalds$ gcc --version
gcc (Debian 8.3.0-6) 8.3.0
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
mtodorov@domac:~/linux/kernel/linux_torvalds$

Hope this helps.

I lack the insight to pinpoint the exact fault in the patch.

Regards,