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

[Mirsad Goran Todorovac]

On 12. 01. 2023. 20:50, Mirsad Todorovac wrote:
> 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@xxxxxxxxxx>
> 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.

P.S.

To further complicate things, on Ubuntu 22.10 Lenovo Ideapad 3 15ITL6 laptop
the kmemleak stack backtrace is printed correctly with the same kernels
(but .deb instead of .rpm for the same build):

unreferenced object 0xffff94ca88e042d0 (size 80):
  comm "thermald", pid 768, jiffies 4294893592 (age 78581.504s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 0d 01 2d 00 00 00 00 00  ..........-.....
    af 07 01 80 fd ac ff ff 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<ffffffffa0dcb921>] slab_post_alloc_hook+0x91/0x320
    [<ffffffffa0dcfb79>] kmem_cache_alloc+0x169/0x2f0
    [<ffffffffa12b1def>] acpi_os_acquire_object+0x2c/0x32
    [<ffffffffa12b1ea2>] acpi_ps_alloc_op+0x4a/0x99
    [<ffffffffa12af5c8>] acpi_ps_get_next_arg+0x611/0x761
    [<ffffffffa12afbbc>] acpi_ps_parse_loop+0x494/0x8d7
    [<ffffffffa12b1434>] acpi_ps_parse_aml+0x1bb/0x561
    [<ffffffffa12b24c8>] acpi_ps_execute_method+0x20f/0x2d5
    [<ffffffffa12a7acf>] acpi_ns_evaluate+0x34d/0x4f3
    [<ffffffffa12ad6a3>] acpi_evaluate_object+0x180/0x3ae
    [<ffffffffa1269ca8>] acpi_run_osc+0x128/0x250
    [<ffffffffc0bbb14f>] int3400_thermal_run_osc+0x6f/0xc0 [int3400_thermal]
    [<ffffffffc0bbb293>] current_uuid_store+0xe3/0x120 [int3400_thermal]
    [<ffffffffa13b8ed4>] dev_attr_store+0x14/0x30
    [<ffffffffa0ee0458>] sysfs_kf_write+0x38/0x50
    [<ffffffffa0edf516>] kernfs_fop_write_iter+0x146/0x1d0
You have new mail in /var/mail/root
root@marvin-IdeaPad-3-15ITL6:/home/marvin# 

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
The European Union