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

[Mirsad Todorovac <mirsad.todorovac@alu.unizg.hr>]

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Hi all,

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.

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,
Mirsad

-- 
Mirsad Goran Todorovac
Sistem inženjer
Grafički fakultet | Akademija likovnih umjetnosti
Sveučilište u Zagrebu

System engineer
Faculty of Graphic Arts | Academy of Fine Arts
University of Zagreb, Republic of Croatia

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