Re: sched: WARNING: at include/linux/cpumask.h:108 select_fallback_rq+0x241/0x280()

Peter Zijlstra
2012-04-14T18:12:42Z

On Sat, 2012-04-14 at 13:40 +0200, Sasha Levin wrote:
> On Sat, Apr 14, 2012 at 11:17 AM, Peter Zijlstra <peterz@infradead.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