Re: [linus:master] [timers/migration] 10a0e6f3d3: BUG:KCSAN:data-race_in__tmigr_cpu_activate/print_report

[Frederic Weisbecker <frederic@kernel.org>]

Le Fri, Jan 03, 2025 at 04:24:52PM +0800, kernel test robot a écrit :
> 
> 
> Hello,
> 
> kernel test robot noticed "BUG:KCSAN:data-race_in__tmigr_cpu_activate/print_report" on:
> 
> commit: 10a0e6f3d3db7dcfe36e578923e5f038f1d2b72a ("timers/migration: Move hierarchy setup into cpuhotplug prepare callback")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> 
> [test failed on linus/master      ccb98ccef0e543c2bd4ef1a72270461957f3d8d0]
> [test failed on linux-next/master 8155b4ef3466f0e289e8fcc9e6e62f3f4dceeac2]
> 
> in testcase: trinity
> version: 
> with following parameters:
> 
> 	runtime: 300s
> 	group: group-00
> 	nr_groups: 5
> 
> 
> 
> config: x86_64-randconfig-003-20241231
> compiler: gcc-12
> test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
> 
> (please refer to attached dmesg/kmsg for entire log/backtrace)
> 
> 
> we observed the issue happens randomly, but keeps clean on parent.
> 
> 
> facd40aa5c4699f9 10a0e6f3d3db7dcfe36e578923e
> ---------------- ---------------------------
>        fail:runs  %reproduction    fail:runs
>            |             |             |
>            :48          17%           8:48    dmesg.BUG:KCSAN:data-race_in__tmigr_cpu_activate/print_report
> 
> 
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <oliver.sang@intel.com>
> | Closes: https://lore.kernel.org/oe-lkp/202501031612.62e0c498-lkp@intel.com
> 
> 
> [   30.027314][    T0] BUG: KCSAN: data-race in __tmigr_cpu_activate / print_report
> [   30.027314][    T0]
> [   30.027314][    T0] write to 0xffff88842fc28004 of 1 bytes by task 0 on cpu 0:
> [ 30.027314][ T0] __tmigr_cpu_activate (kernel/time/timer_migration.c:689)
> [ 30.027314][ T0] tmigr_cpu_activate (kernel/time/timer_migration.c:713)
> [ 30.027314][ T0] timer_clear_idle (kernel/time/timer.c:2380 (discriminator 22))
> [ 30.027314][ T0] tick_nohz_restart_sched_tick (kernel/time/tick-sched.c:1097)
> [ 30.027314][ T0] tick_nohz_idle_exit (kernel/time/tick-sched.c:1442 kernel/time/tick-sched.c:1483)
> [ 30.027314][ T0] do_idle (arch/x86/include/asm/bitops.h:75 include/linux/sched/idle.h:36 kernel/sched/idle.c:346)
> [ 30.027314][ T0] cpu_startup_entry (kernel/sched/idle.c:429 (discriminator 1))
> [ 30.027314][ T0] kernel_init (init/main.c:1459)
> [ 30.027314][ T0] do_initcalls (init/main.c:1333)
> [ 30.027314][ T0] clear_bss (arch/x86/kernel/head64.c:381)
> [ 30.027314][ T0] reserve_bios_regions (arch/x86/kernel/ebda.c:57)
> [ 30.027314][ T0] common_startup_64 (arch/x86/kernel/head_64.S:421)
> [   30.027314][    T0]
> [   30.027314][    T0] read to 0xffff88842fc28004 of 1 bytes by task 0 on cpu 1:
> [ 30.027314][ T0] print_report (kernel/kcsan/report.c:395)
> [ 30.027314][ T0] kcsan_report_known_origin (kernel/kcsan/report.c:504 kernel/kcsan/report.c:694)
> [ 30.027314][ T0] kcsan_setup_watchpoint (kernel/kcsan/core.c:678)
> [ 30.027314][ T0] tmigr_next_groupevt (kernel/time/timer_migration.c:576)
> [ 30.027314][ T0] tmigr_update_events (kernel/time/timer_migration.c:618 kernel/time/timer_migration.c:853)
> [ 30.027314][ T0] tmigr_inactive_up (kernel/time/timer_migration.c:1327)

It looks like the .ignore flag accesses and I think it should be tagged as a
voluntary data_race().

Let me cook a patch for that.

Thanks.