[PATCH] kernel/kexec: remove the lock operation of system_transition_mutex

[Rafael J. Wysocki]

On Mon, Jan 25, 2021 at 10:05 AM Pingfan Liu <kernelfans at gmail.com> wrote:
>
> On Fri, Jan 22, 2021 at 3:42 PM Baoquan He <bhe at redhat.com> wrote:
> >
> > Function kernel_kexec() is called with lock system_transition_mutex held
> > in reboot system call. While inside kernel_kexec(), it will acquire
> > system_transition_mutex agin. This will lead to dead lock.
> >
> > The dead lock should be easily triggered, it hasn't caused any failure
> > report just because the feature 'kexec jump' is almost not used by anyone
> > as far as I know. An inquiry can be made about who is using 'kexec jump'
> > and where it's used. Before that, let's simply remove the lock operation
> > inside CONFIG_KEXEC_JUMP ifdeffery scope.
> >
> > Signed-off-by: Baoquan He <bhe at redhat.com>
> > Reported-by: Dan Carpenter <dan.carpenter at oracle.com>
> > Reviewed-by: Pingfan Liu <kernelfans at gmail.com>
> > ---
> >  kernel/kexec_core.c | 2 --
> >  1 file changed, 2 deletions(-)
> >
> > 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();
> >         }
> >  #endif
> >
> > --
> > 2.17.2
> >
> Reviewed-by: Pingfan Liu <kernelfans at gmail.com>

Applied as 5.11-rc material, thanks!