[bug report] PM / reboot: Eliminate race between reboot and suspend

[Pingfan Liu]

On Wed, Jan 20, 2021 at 5:30 PM Baoquan He <bhe at redhat.com> wrote:
>
> Hi,
>
> On 11/18/20 at 09:59pm, Dan Carpenter wrote:
> > Hello Pingfan Liu,
> >
> > The patch 55f2503c3b69: "PM / reboot: Eliminate race between reboot
> > and suspend" from Jul 31, 2018, leads to the following static checker
> > warning:
> >
> >       kernel/power/main.c:27 lock_system_sleep()
> >       warn: called with lock held.  '&system_transition_mutex'
>
> This is a good finding. I think we can simply remove the lock/unlock
> pair of system_transition_mutex in kernel_kexec() function. The dead
> lock should be easily triggered, but it hasn't caused any failure report
> because the feature 'kexec jump' is almost not used by anyone as far as
> I know. We may need to find out who is using it and where it's used
> through an inquiry. Before that, we can just remove the lock operation
> inside CONFIG_KEXEC_JUMP ifdeffery scope. Thanks.
>
>
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index 80905e5aa8ae..a0b6780740c8 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -1134,7 +1134,6 @@ int kernel_kexec(void)
>
>  #ifdef CONFIG_KEXEC_JUMP
>         if (kexec_image->preserve_context) {
> -               lock_system_sleep();
>                 pm_prepare_console();
>                 error = freeze_processes();
>                 if (error) {
> @@ -1197,7 +1196,6 @@ int kernel_kexec(void)
>                 thaw_processes();
>   Restore_console:
>                 pm_restore_console();
> -               unlock_system_sleep();

This should work since the only caller syscall_reboot has already
placed kernel_kexec() under the protection of system_transition_mutex.

Thanks for the fix.

Reviewed-by: Pingfan Liu <kernelfans at gmail.com>