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Date: Sun, 25 May 2014 10:16:39 +0200
From: Mike Galbraith <umgwanakikbuti@...il.com>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: linux-rt-users <linux-rt-users@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>, rostedt@...dmis.org,
John Kacur <jkacur@...hat.com>
Subject: [patch v2] rt/sched: fix resursion when CONTEXT_TRACKING and
PREEMPT_LAZY are enabled
On Fri, 2014-05-16 at 15:53 +0200, Mike Galbraith wrote:
> On Tue, 2014-05-13 at 17:40 +0200, Sebastian Andrzej Siewior wrote:
> > * Mike Galbraith | 2014-05-10 06:15:03 [+0200]:
> >
> > >On Fri, 2014-05-09 at 20:12 +0200, Sebastian Andrzej Siewior wrote:
> > >
> > >> Known issues:
> > >>
> > >> - bcache is disabled.
> > >>
> > >> - lazy preempt on x86_64 leads to a crash with some load.
> > >
> > >That is only with NO_HZ_FUL enabled here. Box blows the stack during
> > >task exit, eyeballing hasn't spotted the why.
> >
> > Even if I disable NO_HZ_FULL it explodes as soon as hackbench starts.
>
> Ah, you didn't turn CONTEXT_TRACKING off too. The below made the dirty
> little SOB die here.
Something obviously went wrong with retest after deciding to do..
> --- a/include/linux/preempt_mask.h
> +++ b/include/linux/preempt_mask.h
> @@ -118,9 +118,15 @@ extern int in_serving_softirq(void);
> ((preempt_count() & ~PREEMPT_ACTIVE) != PREEMPT_CHECK_OFFSET)
>
> #ifdef CONFIG_PREEMPT_COUNT
> -# define preemptible() (preempt_count() == 0 && !irqs_disabled())
> +# define preemptible() (preempt_count() == 0 && !irqs_disabled())
> +#ifdef CONFIG_PREEMPT_LAZY
> +# define preemptible_lazy() (preempt_lazy_count() !=0 && !need_resched_now())
ahem ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
..that preemptible_lazy() bit. Turn that back right side up.
(or you can do something completely different, like make it just not go
there ala 12-rt, or do the fold thing for rt as well, vs flag being set
meaning try to schedule and bail if not allowed [as usual])
If context tracking is enabled, we can recurse, and explode violently.
Add missing checks to preempt_schedule_context().
Fix other inconsistencies spotted while searching for the little SOB.
Signed-off-by: Mike Galbraith <umgwanakikbuti@...il.com>
---
arch/x86/include/asm/thread_info.h | 1 +
include/linux/preempt.h | 2 +-
include/linux/preempt_mask.h | 10 ++++++++--
kernel/context_tracking.c | 2 +-
kernel/fork.c | 1 +
kernel/sched/core.c | 16 +++++-----------
kernel/sched/fair.c | 2 +-
7 files changed, 18 insertions(+), 16 deletions(-)
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -51,6 +51,7 @@ struct thread_info {
.flags = 0, \
.cpu = 0, \
.saved_preempt_count = INIT_PREEMPT_COUNT, \
+ .preempt_lazy_count = 0, \
.addr_limit = KERNEL_DS, \
.restart_block = { \
.fn = do_no_restart_syscall, \
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -91,8 +91,8 @@ do { \
#define preempt_lazy_enable() \
do { \
- dec_preempt_lazy_count(); \
barrier(); \
+ dec_preempt_lazy_count(); \
preempt_check_resched(); \
} while (0)
--- a/include/linux/preempt_mask.h
+++ b/include/linux/preempt_mask.h
@@ -118,9 +118,15 @@ extern int in_serving_softirq(void);
((preempt_count() & ~PREEMPT_ACTIVE) != PREEMPT_CHECK_OFFSET)
#ifdef CONFIG_PREEMPT_COUNT
-# define preemptible() (preempt_count() == 0 && !irqs_disabled())
+# define preemptible() (preempt_count() == 0 && !irqs_disabled())
+#ifdef CONFIG_PREEMPT_LAZY
+# define preemptible_lazy() (preempt_lazy_count() == 0 || need_resched_now())
#else
-# define preemptible() 0
+# define preemptible_lazy() 1
+#endif
+#else
+# define preemptible() 0
+# define preemptible_lazy() 0
#endif
#endif /* LINUX_PREEMPT_MASK_H */
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -124,7 +124,7 @@ asmlinkage void __sched notrace preempt_
{
enum ctx_state prev_ctx;
- if (likely(!preemptible()))
+ if (likely(!preemptible() || !preemptible_lazy()))
return;
/*
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -329,6 +329,7 @@ static struct task_struct *dup_task_stru
setup_thread_stack(tsk, orig);
clear_user_return_notifier(tsk);
clear_tsk_need_resched(tsk);
+ clear_tsk_need_resched_lazy(tsk);
stackend = end_of_stack(tsk);
*stackend = STACK_END_MAGIC; /* for overflow detection */
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2866,8 +2866,8 @@ void migrate_enable(void)
p->migrate_disable = 0;
unpin_current_cpu();
- preempt_enable();
preempt_lazy_enable();
+ preempt_enable();
}
EXPORT_SYMBOL(migrate_enable);
#else
@@ -3101,19 +3101,13 @@ asmlinkage void __sched notrace preempt_
{
/*
* If there is a non-zero preempt_count or interrupts are disabled,
- * we do not want to preempt the current task. Just return..
+ * we do not want to preempt the current task. Just return. For
+ * lazy preemption we also check for non-zero preempt_count_lazy,
+ * and bail if no immediate preemption is required.
*/
- if (likely(!preemptible()))
+ if (likely(!preemptible() || !preemptible_lazy()))
return;
-#ifdef CONFIG_PREEMPT_LAZY
- /*
- * Check for lazy preemption
- */
- if (current_thread_info()->preempt_lazy_count &&
- !test_thread_flag(TIF_NEED_RESCHED))
- return;
-#endif
do {
__preempt_count_add(PREEMPT_ACTIVE);
/*
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4447,7 +4447,7 @@ static void check_preempt_wakeup(struct
* prevents us from potentially nominating it as a false LAST_BUDDY
* below.
*/
- if (test_tsk_need_resched(curr))
+ if (test_tsk_need_resched(curr) || test_tsk_need_resched_lazy(curr))
return;
/* Idle tasks are by definition preempted by non-idle tasks. */
--
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