KCSAN: data-race in tick_nohz_stop_tick / tick_sched_timer

[Kaia Yadira]

Hello,

When using Syzkaller to fuzz the latest Linux kernel, the following
crash was triggered.

HEAD commit: a7904a538933 Linux 5.16-rc6
git tree: upstream
console output: KCSAN: data-race in tick_nohz_stop_tick / tick_nohz_stop_tick
kernel config: https://paste.ubuntu.com/p/QB39MJKWKb/plain/
Syzlang reproducer: https://paste.ubuntu.com/p/T25kYMrytM/plain/

If you fix this issue, please add the following tag to the commit:

Reported-by: Hypericum <hypericumperforatum4444@xxxxxxxxx>

I think there are two threads visiting the variable tick_do_timer_cpu
at kernel/time/tick-sched.c:191 and 872 without locking.

reproducer log: https://paste.ubuntu.com/p/942c3QpFDJ/plain/
report:
==================================================================
BUG: KCSAN: data-race in tick_nohz_stop_tick / tick_sched_timer

write to 0xffffffff85ebf1e0 of 4 bytes by task 0 on cpu 6:
 tick_nohz_stop_tick+0xa5/0x410 kernel/time/tick-sched.c:873
 __tick_nohz_idle_stop_tick kernel/time/tick-sched.c:1062 [inline]
 tick_nohz_idle_stop_tick+0xde/0x1a0 kernel/time/tick-sched.c:1083
 cpuidle_idle_call kernel/sched/idle.c:192 [inline]
 do_idle+0xe3/0x250 kernel/sched/idle.c:306
 cpu_startup_entry+0x15/0x20 kernel/sched/idle.c:403
 secondary_startup_64_no_verify+0xb1/0xbb

read to 0xffffffff85ebf1e0 of 4 bytes by interrupt on cpu 1:
 tick_sched_do_timer kernel/time/tick-sched.c:187 [inline]
 tick_sched_timer+0x41/0x210 kernel/time/tick-sched.c:1421
 __run_hrtimer+0x133/0x420 kernel/time/hrtimer.c:1685
 __hrtimer_run_queues kernel/time/hrtimer.c:1749 [inline]
 hrtimer_interrupt+0x36e/0xa80 kernel/time/hrtimer.c:1811
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1086 [inline]
 __sysvec_apic_timer_interrupt+0xa3/0x250 arch/x86/kernel/apic/apic.c:1103
 sysvec_apic_timer_interrupt+0x88/0xb0 arch/x86/kernel/apic/apic.c:1097
 asm_sysvec_apic_timer_interrupt+0x12/0x20
 native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
 arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
 default_idle+0xb/0x10 arch/x86/kernel/process.c:733
 default_idle_call+0x28/0xd0 kernel/sched/idle.c:112
 cpuidle_idle_call kernel/sched/idle.c:194 [inline]
 do_idle+0xe8/0x250 kernel/sched/idle.c:306
 cpu_startup_entry+0x15/0x20 kernel/sched/idle.c:403
 secondary_startup_64_no_verify+0xb1/0xbb

value changed: 0x00000006 -> 0xffffffff

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.16.0-rc8+ #11
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
==================================================================