Re: [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM

Peter Zijlstra
2011-05-26T16:05:49Z

On Thu, 2011-05-26 at 17:59 +0200, Peter Zijlstra wrote:
> On Thu, 2011-05-26 at 17:45 +0200, Oleg Nesterov wrote:
> > Stupid question. Can't we fix this problem if we do
> >
> > - if (p == current)
> > + if (cpu == raw_smp_processor_id())
> >
> > ?
> >
> > I forgot the rules... but iirc task_cpu(p) can't be changed under us?
>
> Easy enough to test.. brain gave out again,. hold on ;-)

The below seems to run all-right so far, I'll let it run for a while.

---
arch/x86/include/asm/system.h | 2 ++
kernel/sched.c | 3 ++-
kernel/sched_debug.c | 7 +++++++
3 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h
index c2ff2a1..2c597e8 100644
--- a/arch/x86/include/asm/system.h
+++ b/arch/x86/include/asm/system.h
@@ -10,6 +10,8 @@
#include <linux/kernel.h>
#include <linux/irqflags.h>

+#define __ARCH_WANT_INTERRUPTS_ON_CTXSW
+
/* entries in ARCH_DLINFO: */
#if defined(CONFIG_IA32_EMULATION) || !defined(CONFIG_X86_64)
# define AT_VECTOR_SIZE_ARCH 2
diff --git a/kernel/sched.c b/kernel/sched.c
index 2d12893..f3627e5 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2636,7 +2636,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
* to spin on ->on_cpu if p is current, since that would
* deadlock.
*/
- if (p == current) {
+ if (cpu == smp_processor_id()) {
+ p->sched_contributes_to_load = 0;
ttwu_queue(p, cpu);
goto stat;
}
diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index a6710a1..f0ff1de 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -332,6 +332,13 @@ static int sched_debug_show(struct seq_file *m, void *v)
(int)strcspn(init_utsname()->version, " "),
init_utsname()->version);

+#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
+ SEQ_printf(m, "__ARCH_WANT_INTERRUPTS_ON_CTXSW\n");
+#endif
+#ifdef __ARCH_WANT_UNLOCKED_CTXSW
+ SEQ_printf(m, "__ARCH_WANT_UNLOCKED_CTXSW\n");
+#endif
+
#define P(x) \
SEQ_printf(m, "%-40s: %Ld\n", #x, (long long)(x))
#define PN(x) \