linux-kernel - Re: sched: WARNING: at include/linux/cpumask.h:108 select_fallback

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Date:	Sat, 14 Apr 2012 20:12:19 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>, mingo@...nel.org,
	"Liu, Chuansheng" <chuansheng.liu@...el.com>, vapier@...too.org,
	rusty@...tcorp.com.au
Subject: Re: sched: WARNING: at include/linux/cpumask.h:108
 select_fallback_rq+0x241/0x280()

On Sat, 2012-04-14 at 13:40 +0200, Sasha Levin wrote:
> On Sat, Apr 14, 2012 at 11:17 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Sat, 2012-03-31 at 13:22 +0530, Srivatsa S. Bhat wrote:
> >>
> >> One of the perils of using macros instead of true function calls :-(
> >>
> > You can do type checking in macros too, its not pretty, but there's
> > several such things already, see min()/max() for example.
> 
> Would it make sense to somehow standardize type checking in kernel
> macros? Possibly a set of wrappers that would make type checking easy
> to get into new and existing macros?


I had a quick go with the below and that doesn't quite work for no
obvious reasons as of yet.. Also, that call out to cpumask_next() should
already do type validation for us, so still no clue why my earlier code
compiled at all.

---
 include/linux/cpumask.h |    1 +
 include/linux/kernel.h  |   10 ++++++++++
 2 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index a2c819d..aec8355 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -201,6 +201,7 @@ int cpumask_any_but(const struct cpumask *mask, unsigned int cpu);
  * After the loop, cpu is >= nr_cpu_ids.
  */
 #define for_each_cpu(cpu, mask)				\
+	match_type(const struct cpumask *, (mask));	\
 	for ((cpu) = -1;				\
 		(cpu) = cpumask_next((cpu), (mask)),	\
 		(cpu) < nr_cpu_ids;)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 645231c..bcb7da3 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -549,6 +549,16 @@ ftrace_vprintk(const char *fmt, va_list ap)
 static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
 #endif /* CONFIG_TRACING */
 
+#define match_type_type(t1, t2)			\
+do {						\
+	t1 uninitialized_var(____t1);		\
+	t2 uninitialized_var(____t2);		\
+	(void) (&____t1 == &____t2);		\
+} while (0)
+
+#define match_type(t, v)			\
+	match_type_type(t, typeof(v))
+
 /*
  * min()/max()/clamp() macros that also do
  * strict type-checking.. See the

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