Re: [PATCH 1/1] hung_task: fix objtool sibling call warning in watchdog()

[Lance Yang]

On 2025/8/1 01:59, Nathan Chancellor wrote:
> On Thu, Jul 31, 2025 at 10:39:34AM +0800, Lance Yang wrote:
> > From: Lance Yang <lance.yang@xxxxxxxxx>
> >
> > The kernel test robot reported an objtool warning on the loongarch
> > architecture with clang:
> >
> >          vmlinux.o: warning: objtool: watchdog+0x418: sibling call from
> > callable instruction with modified stack frame
> >
> > To resolve this, explicitly prevent the compiler from inlining or
> > performing a tail call on check_hung_uninterruptible_tasks() by marking
> > it with the noinline attribute. This ensures a standard function call
> > with a proper stack frame, satisfying objtool's validation requirements.
> >
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > Closes: https://lore.kernel.org/oe-kbuild-all/202507301256.cZlxQ10s-lkp@xxxxxxxxx/
> > Signed-off-by: Lance Yang <lance.yang@xxxxxxxxx>
>
> While this may solve that particular instance of the warning, the fact
> there are many, many more with that configuration indicates that there
> will need to be a more generalized fix. I have started a separate thread
> with some LoongArch folks around this issue:

Thanks for the heads-up!

Yes, you're right, a more general fix is definitely the way to go.

I'll keep an eye on that thread and see how I can help ;)

Thanks,
Lance

> https://lore.kernel.org/20250731175655.GA1455142@ax162/
>
> Cheers,
> Nathan
>
> > ---
> >   kernel/hung_task.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> > index 8708a1205f82..a5b5a0a2c262 100644
> > --- a/kernel/hung_task.c
> > +++ b/kernel/hung_task.c
> > @@ -283,7 +283,7 @@ static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
> >    * a really long time (120 seconds). If that happens, print out
> >    * a warning.
> >    */
> > -static void check_hung_uninterruptible_tasks(unsigned long timeout)
> > +static noinline void check_hung_uninterruptible_tasks(unsigned long timeout)
> >   {
> >   	int max_count = sysctl_hung_task_check_count;
> >   	unsigned long last_break = jiffies;
> > --
> > 2.49.0