KCSAN: data-race in tick_nohz_stop_tick / tick_nohz_stop_tick

[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/Xtr5t49Jv6/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 visit the variable tick_do_timer_cpu
without locking.

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

write to 0xffffffff85ebf1e0 of 4 bytes by task 0 on cpu 7:
 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 task 0 on cpu 0:
 tick_nohz_stop_tick+0x7f/0x410 kernel/time/tick-sched.c:872
 __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
 rest_init+0xed/0xf0 init/main.c:725
 arch_call_rest_init+0xa/0xb
 start_kernel+0x5de/0x663 init/main.c:1135
 secondary_startup_64_no_verify+0xb1/0xbb

value changed: 0x00000007 -> 0xffffffff

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