Subject: [PATCH] stacktrace: Provide stack_trace_save_tsk() stub in the !CONFIG_STACKTRACE case too

From: Ingo Molnar <[email-masked]>
Date: Fri, 22 Oct 2021 09:43:50 +0200

* Qi Zheng <[email-masked]> wrote:

> 
> 
> On 10/18/21 2:23 PM, Stephen Rothwell wrote:
> > Hi all,
> > 
> > After merging the tip tree, today's linux-next build (x86_64 allnoconfig)
> > failed like this:
> > 
> > arch/x86/kernel/process.c: In function '__get_wchan':
> > arch/x86/kernel/process.c:950:2: error: implicit declaration of function 'stack_trace_save_tsk' [-Werror=implicit-function-declaration]
> >    950 |  stack_trace_save_tsk(p, &entry, 1, 0);
> >        |  ^~~~~~~~~~~~~~~~~~~~
> > cc1: some warnings being treated as errors
> > 
> > Caused by commit
> > 
> >    bc9bbb81730e ("x86: Fix get_wchan() to support the ORC unwinder")
> > 
> > stack_trace_save_tsk() requires CONFIG_STACKTRACE which is not set for
> > this build.
> 
> Maybe get_wchan() can be updated to:
> 
> unsigned long get_wchan(struct task_struct *p)
> {
> #ifdef CONFIG_STACKTRACE
> 	unsigned long entry = 0;
> 
> 	stack_trace_save_tsk(p, &entry, 1, 0);
> 	return entry;
> #else /* CONFIG_STACKTRACE */
> 	return 0;
> #endif
> }

And repeat the same ugliness in every single function that happens to use 
the stack_trace_save_tsk() API??

The correct solution is to define stack_trace_save_tsk() in the 
!CONFIG_STACKTRACE case too, as the patch below does.

Thanks,

	Ingo

==============================>
From: Ingo Molnar <[email-masked]>
Date: Fri, 22 Oct 2021 09:40:27 +0200
Subject: [PATCH] stacktrace: Provide stack_trace_save_tsk() stub in the !CONFIG_STACKTRACE case too

The following commit:

  bc9bbb81730e ("x86: Fix get_wchan() to support the ORC unwinder")

Added stack_trace_save_tsk() use to __get_wchan(), while this method is not
unconditionally defined: it's not available in the !CONFIG_STACKTRACE case.

Give a default implementation that does nothing.

Reported-by: Stephen Rothwell <[email-masked]>
Fixes: bc9bbb81730e ("x86: Fix get_wchan() to support the ORC unwinder")
Cc: Qi Zheng <[email-masked]>
Cc: Peter Zijlstra <[email-masked]>
Signed-off-by: Ingo Molnar <[email-masked]>
---
 include/linux/stacktrace.h | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/include/linux/stacktrace.h b/include/linux/stacktrace.h
index 9edecb494e9e..3ccaf599630f 100644
--- a/include/linux/stacktrace.h
+++ b/include/linux/stacktrace.h
@@ -91,8 +91,19 @@ extern void save_stack_trace_tsk(struct task_struct *tsk,
 extern int save_stack_trace_tsk_reliable(struct task_struct *tsk,
 					 struct stack_trace *trace);
 extern void save_stack_trace_user(struct stack_trace *trace);
+
 #endif /* !CONFIG_ARCH_STACKWALK */
-#endif /* CONFIG_STACKTRACE */
+
+#else /* !CONFIG_STACKTRACE: */
+static inline unsigned int
+stack_trace_save_tsk(struct task_struct *task,
+		     unsigned long *store, unsigned int size,
+		     unsigned int skipnr)
+{
+	return -ENOSYS;
+}
+
+#endif /* !CONFIG_STACKTRACE */
 
 #if defined(CONFIG_STACKTRACE) && defined(CONFIG_HAVE_RELIABLE_STACKTRACE)
 int stack_trace_save_tsk_reliable(struct task_struct *tsk, unsigned long *store,