Re: [BUG] KCSAN: data-race in _find_next_bit+0x42/0xf0

[Mirsad Todorovac]

On 8/17/23 22:29, Mirsad Todorovac wrote:
> Hi,
>
> This is your friendly bug reporter :-)
>
> This is probably the last one for today from the KCSAN series.
>
> The setup is vanilla torvalds kernel, Ubuntu 22.04 LTS and a Ryzen 7950X box.
>
> NOTE: There are no proprietary modules to my knowledge, the Canonical Livepatch did not work for this
> kernel, but I suspect the taint was turned on by the previous instances of bugs.
>
> Please find complete dmesg output and lshw output attached.
>
> dmesg output except:
>
> [10026.864497] ==================================================================
> [10026.864516] BUG: KCSAN: data-race in _find_next_bit+0x42/0xf0
>
> [10026.864544] race at unknown origin, with read to 0xffff9b7440075408 of 8 bytes by interrupt on cpu 0:
> [10026.864562]  _find_next_bit+0x42/0xf0
> [10026.864577]  _nohz_idle_balance.isra.0+0x1ff/0x3f0
> [10026.864594]  run_rebalance_domains+0x75/0x90
> [10026.864610]  __do_softirq+0xda/0x330
> [10026.864626]  __irq_exit_rcu+0x75/0xa0
> [10026.864640]  irq_exit_rcu+0xe/0x20
> [10026.864654]  sysvec_call_function_single+0x96/0xb0
> [10026.864671]  asm_sysvec_call_function_single+0x1b/0x20
> [10026.864690]  cpuidle_enter_state+0x1df/0x520
> [10026.864709]  cpuidle_enter+0x41/0x70
> [10026.864725]  call_cpuidle+0x23/0x60
> [10026.864742]  do_idle+0x1f1/0x250
> [10026.864754]  cpu_startup_entry+0x20/0x30
> [10026.864767]  rest_init+0x121/0x140
> [10026.864786]  arch_call_rest_init+0xe/0x30
> [10026.864803]  start_kernel+0x8e3/0xd70
> [10026.864819]  x86_64_start_reservations+0x18/0x30
> [10026.864835]  x86_64_start_kernel+0xc0/0x110
> [10026.864848]  secondary_startup_64_no_verify+0x17e/0x18b
>
> [10026.864876] value changed: 0x00000000ffffffcf -> 0x00000000ffffffff
>
> [10026.864897] Reported by Kernel Concurrency Sanitizer on:
> [10026.864908] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G             L     6.5.0-rc6-net-cfg-kcsan-00038-g16931859a650 #35
> [10026.864926] Hardware name: ASRock X670E PG Lightning/X670E PG Lightning, BIOS 1.21 04/26/2023
> [10026.864936] ==================================================================

P.S.

By Mr. Heo's instructions, I am adding the decoded stacktrace to this bug report, which ought to have been
done in the first place.

Apology for the inconvenience.

[ 1092.112020] ==================================================================
[ 1092.112039] BUG: KCSAN: data-race in _find_next_bit (lib/find_bit.c:133 (discriminator 2))

[ 1092.112068] race at unknown origin, with read to 0xffff963d80075a38 of 8 bytes by interrupt on cpu 0:
[ 1092.112086] _find_next_bit (lib/find_bit.c:133 (discriminator 2))
[ 1092.112102] _nohz_idle_balance.isra.0 (./include/linux/find.h:430 kernel/sched/fair.c:11676)
[ 1092.112119] run_rebalance_domains (kernel/sched/fair.c:11969)
[ 1092.112136] __do_softirq (kernel/softirq.c:553)
[ 1092.112152] __irq_exit_rcu (kernel/softirq.c:427 kernel/softirq.c:632)
[ 1092.112167] irq_exit_rcu (kernel/softirq.c:647)
[ 1092.112181] sysvec_call_function_single (arch/x86/kernel/smp.c:287 (discriminator 14))
[ 1092.112198] asm_sysvec_call_function_single (./arch/x86/include/asm/idtentry.h:653)
[ 1092.112218] cpuidle_enter_state (drivers/cpuidle/cpuidle.c:291)
[ 1092.112238] cpuidle_enter (drivers/cpuidle/cpuidle.c:390)
[ 1092.112254] call_cpuidle (kernel/sched/idle.c:135)
[ 1092.112271] do_idle (kernel/sched/idle.c:219 kernel/sched/idle.c:282)
[ 1092.112284] cpu_startup_entry (kernel/sched/idle.c:378 (discriminator 1))
[ 1092.112298] rest_init (./include/linux/cpumask.h:1058 init/main.c:700)
[ 1092.112311] arch_call_rest_init+0xe/0x30
[ 1092.112326] start_kernel (init/main.c:833 init/main.c:909)
[ 1092.112340] x86_64_start_reservations (arch/x86/kernel/head64.c:544)
[ 1092.112356] x86_64_start_kernel (arch/x86/kernel/head64.c:486 (discriminator 17))
[ 1092.112368] secondary_startup_64_no_verify (arch/x86/kernel/head_64.S:441)

[ 1092.112388] value changed: 0x00000000fbffffff -> 0x00000000fbfffffd

[ 1092.112402] Reported by Kernel Concurrency Sanitizer on:
[ 1092.112410] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G             L     6.5.0-rc6+ #44
[ 1092.112422] Hardware name: ASRock X670E PG Lightning/X670E PG Lightning, BIOS 1.21 04/26/2023
[ 1092.112429] ==================================================================

I should probably take a break while this is being investigated.

Best regards,
Mirsad Todorovac