Re: [PATCH] arm64: suspend: Only track cpuidle context for idle tasks

[Catalin Marinas <catalin.marinas@arm.com>]

On Thu, Nov 05, 2026 at 08:19:45PM +0000, syzbot wrote:
> From: Uladzislau Zhauniarovich <uladzislau.zhauniarovich@gmail.com>
> 
> Commit 19235e472798 ("cpuidle, arm64: Fix the ARM64 cpuidle logic") moved
> the calls to ct_cpuidle_enter() and ct_cpuidle_exit() into cpu_suspend() so
> that arm64 cpuidle could keep RCU watching longer and manage context
> tracking internally. However, cpu_suspend() is called not only by cpuidle
> via psci_cpu_suspend_enter() (which runs in the context of the idle task),
> but also during system suspend via psci_system_suspend_enter() (which runs
> in the context of the task initiating suspend, such as a process writing to
> /sys/power/state).
> 
> When entering system suspend, current is a non-idle task. Calling
> ct_cpuidle_enter() invokes ct_kernel_exit() from kernel space (!user) on a
> non-idle task. With CONFIG_RCU_EQS_DEBUG enabled, this violates context
> tracking invariants and triggers a warning:
> 
> WARNING: kernel/context_tracking.c:120 at ct_kernel_exit+0x1b4/0x1f4
> kernel/context_tracking.c:118
> Call trace:
>  ct_kernel_exit+0x1b4/0x1f4 kernel/context_tracking.c:118
>  ct_idle_enter+0x20/0x34 kernel/context_tracking.c:299
>  ct_cpuidle_enter include/linux/cpuidle.h:134 [inline]
>  cpu_suspend+0x264/0x474 arch/arm64/kernel/suspend.c:136
>  psci_system_suspend_enter+0x4c/0x80 drivers/firmware/psci/psci.c:544
>  suspend_enter kernel/power/suspend.c:468 [inline]
>  suspend_devices_and_enter+0x88c/0xd0c kernel/power/suspend.c:533
>  enter_state kernel/power/suspend.c:618 [inline]
>  pm_suspend+0x498/0x698 kernel/power/suspend.c:644
>  state_store+0x14c/0x1fc kernel/power/main.c:819
>  kobj_attr_store+0x6c/0x90 lib/kobject.c:842
>  sysfs_kf_write+0xe0/0x108 fs/sysfs/file.c:145
>  kernfs_fop_write_iter+0x260/0x3b8 fs/kernfs/file.c:345
>  vfs_write+0x51c/0xa0c fs/read_write.c:687
>  ksys_write+0x12c/0x228 fs/read_write.c:739
> 
> A corresponding warning is subsequently triggered in ct_kernel_enter() via
> ct_cpuidle_exit() upon resume.
> 
> Fix this by checking is_idle_task(current) in cpu_suspend() and only
> invoking ct_cpuidle_enter() and ct_cpuidle_exit() when executing in the
> context of an idle task.
> 
> Fixes: 19235e472798 ("cpuidle, arm64: Fix the ARM64 cpuidle logic")
> Assisted-by: Gemini:gemini-3.8-flash Gemini:gemini-3.1-pro-preview syzbot
> Reported-by: syzbot+79883955da3a62652a80@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=79883955da3a62652a80
> Link: https://syzkaller.appspot.com/ai_job?id=5359e16f-013b-4850-9cbc-ddfb3bac95e5
> Signed-off-by: Uladzislau Zhauniarovich <uladzislau.zhauniarovich@gmail.com>

The patch looks fine to me but the authorship is confusing. It was sent
by a bot, also generated by a bot. Uladzislau tested the earlier RFC
(thanks!) and syzbot decided to make him author while dropping the
Tested-by. The original tested-by:

https://lore.kernel.org/all/3e92ccb0-2952-4317-af4c-45457c15efae@gmail.com/

I don't think #syz upstream should automatically translate to
Signed-off-by.

What do we even do with such bot-generated fixes (which may be correct,
so can't be entirely ignored)?

-- 
Catalin