Re: next-20240712: task_work.c:(.text+0xc2): undefined reference to `irq_work_queue'

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Jul 12, 2024 at 02:28:38PM +0200, Arnd Bergmann wrote:
> On Fri, Jul 12, 2024, at 14:13, Naresh Kamboju wrote:
> > The 32-bit arm, mips and powerpc the tinyconfig builds failed on today's
> > Linux next-20240712 tag with gcc and clang builds.
> > The defconfig builds pass.
> >
> >   GOOD: next-20240711
> >   BAD:  next-20240712
> >
> > Build error:
> > ------
> > arm-linux-gnueabihf-ld: kernel/task_work.o: in function `task_work_add':
> > task_work.c:(.text+0xc2): undefined reference to `irq_work_queue'
> >
> > Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> 
> The call to this function was added in 466e4d801cd4 ("task_work:
> Add TWA_NMI_CURRENT as an additional notify mode.").  It's possible

Thanks, that initial report was mostly useless without that sha. I do
wonder why 0day build robot didn't complain to me about this. It seems
something it should definitely find.

> that we may have to always enable IRQ_WORK even on non-SMP
> kernels now. In practice it is already enabled in most
> configurations for one reason or another, the the cost is
> likely very small.
> 
> Otherwise checking for CONFIG_HAVE_NMI in the new code might work.

ARM seems to have HAVE_NMI while also being one of the architectures
that is now failing.

I'm a bit confused though, perf is already depending on irq_work (and
perf is the user of TWA_NMI_CURRENT). So I'm not exactly sure what
config fail is leading to all this.

I suppose we can do something like the below.. it'll end up in a runtime
fail for whoever manages to use TWA_NMI_CURRENT without also having
irq_work enabled, but that should currently be nobody.

---
 kernel/task_work.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/task_work.c b/kernel/task_work.c
index 5c2daa7ad3f9..276e245b7e7e 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -81,9 +81,11 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
 	case TWA_SIGNAL_NO_IPI:
 		__set_notify_signal(task);
 		break;
+#ifdef CONFIG_IRQ_WORK
 	case TWA_NMI_CURRENT:
 		irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume));
 		break;
+#endif
 	default:
 		WARN_ON_ONCE(1);
 		break;