[PATCH v7 05/11] task_isolation: add debug boot flag

Chris Metcalf
2015-09-28T15:18:12Z

The new "task_isolation_debug" flag simplifies debugging
of TASK_ISOLATION kernels when processes are running in
PR_TASK_ISOLATION_ENABLE mode. Such processes should get no
interrupts from the kernel, and if they do, when this boot flag is
specified a kernel stack dump on the console is generated.

It's possible to use ftrace to simply detect whether a task_isolation
core has unexpectedly entered the kernel. But what this boot flag
does is allow the kernel to provide better diagnostics, e.g. by
reporting in the IPI-generating code what remote core and context
is preparing to deliver an interrupt to a task_isolation core.

It may be worth considering other ways to generate useful debugging
output rather than console spew, but for now that is simple and direct.

Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>
---
Documentation/kernel-parameters.txt | 7 +++++++
include/linux/isolation.h | 2 ++
kernel/irq_work.c | 5 ++++-
kernel/sched/core.c | 21 +++++++++++++++++++++
kernel/signal.c | 5 +++++
kernel/smp.c | 4 ++++
kernel/softirq.c | 7 +++++++
7 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 22a4b687ea5b..48ff15f3166f 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3623,6 +3623,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
neutralize any effect of /proc/sys/kernel/sysrq.
Useful for debugging.

+ task_isolation_debug [KNL]
+ In kernels built with CONFIG_TASK_ISOLATION and booted
+ in nohz_full= mode, this setting will generate console
+ backtraces when the kernel is about to interrupt a
+ task that has requested PR_TASK_ISOLATION_ENABLE
+ and is running on a nohz_full core.
+
tcpmhash_entries= [KNL,NET]
Set the number of tcp_metrics_hash slots.
Default value is 8192 or 16384 depending on total
diff --git a/include/linux/isolation.h b/include/linux/isolation.h
index 27a4469831c1..9f1747331a36 100644
--- a/include/linux/isolation.h
+++ b/include/linux/isolation.h
@@ -18,11 +18,13 @@ extern void task_isolation_enter(void);
extern void task_isolation_syscall(int nr);
extern void task_isolation_exception(void);
extern void task_isolation_wait(void);
+extern void task_isolation_debug(int cpu);
#else
static inline bool task_isolation_enabled(void) { return false; }
static inline void task_isolation_enter(void) { }
static inline void task_isolation_syscall(int nr) { }
static inline void task_isolation_exception(void) { }
+static inline void task_isolation_debug(int cpu) { }
#endif

static inline bool task_isolation_strict(void)
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index cbf9fb899d92..745c2ea6a4e4 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -17,6 +17,7 @@
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/smp.h>
+#include <linux/isolation.h>
#include <asm/processor.h>

@@ -75,8 +76,10 @@ bool irq_work_queue_on(struct irq_work *work, int cpu)
if (!irq_work_claim(work))
return false;

- if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
+ if (llist_add(&work->llnode, &per_cpu(raised_list, cpu))) {
+ task_isolation_debug(cpu);
arch_send_call_function_single_ipi(cpu);
+ }

return true;
}
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3595403921bd..8ddabb0d7510 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -74,6 +74,7 @@
#include <linux/binfmts.h>
#include <linux/context_tracking.h>
#include <linux/compiler.h>
+#include <linux/isolation.h>

#include <asm/switch_to.h>
#include <asm/tlb.h>
@@ -743,6 +744,26 @@ bool sched_can_stop_tick(void)
}
#endif /* CONFIG_NO_HZ_FULL */

+#ifdef CONFIG_TASK_ISOLATION
+/* Enable debugging of any interrupts of task_isolation cores. */
+static int task_isolation_debug_flag;
+static int __init task_isolation_debug_func(char *str)
+{
+ task_isolation_debug_flag = true;
+ return 1;
+}
+__setup("task_isolation_debug", task_isolation_debug_func);
+
+void task_isolation_debug(int cpu)
+{
+ if (task_isolation_debug_flag && tick_nohz_full_cpu(cpu) &&
+ (cpu_curr(cpu)->task_isolation_flags & PR_TASK_ISOLATION_ENABLE)) {
+ pr_err("Interrupt detected for task_isolation cpu %d\n", cpu);
+ dump_stack();
+ }
+}
+#endif
+
void sched_avg_update(struct rq *rq)
{
s64 period = sched_avg_period();
diff --git a/kernel/signal.c b/kernel/signal.c
index 0f6bbbe77b46..c6e09f0f7e24 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -684,6 +684,11 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
*/
void signal_wake_up_state(struct task_struct *t, unsigned int state)
{
+#ifdef CONFIG_TASK_ISOLATION
+ /* If the task is being killed, don't complain about task_isolation. */
+ if (state & TASK_WAKEKILL)
+ t->task_isolation_flags = 0;
+#endif
set_tsk_thread_flag(t, TIF_SIGPENDING);
/*
* TASK_WAKEKILL also means wake it up in the stopped/traced/killable
diff --git a/kernel/smp.c b/kernel/smp.c
index 07854477c164..b0bddff2693d 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -14,6 +14,7 @@
#include <linux/smp.h>
#include <linux/cpu.h>
#include <linux/sched.h>
+#include <linux/isolation.h>

#include "smpboot.h"

@@ -178,6 +179,7 @@ static int generic_exec_single(int cpu, struct call_single_data *csd,
* locking and barrier primitives. Generic code isn't really
* equipped to do the right thing...
*/
+ task_isolation_debug(cpu);
if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu)))
arch_send_call_function_single_ipi(cpu);

@@ -457,6 +459,8 @@ void smp_call_function_many(const struct cpumask *mask,
}

/* Send a message to all CPUs in the map */
+ for_each_cpu(cpu, cfd->cpumask)
+ task_isolation_debug(cpu);
arch_send_call_function_ipi_mask(cfd->cpumask);

if (wait) {
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 479e4436f787..ed762fec7265 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -24,8 +24,10 @@
#include <linux/ftrace.h>
#include <linux/smp.h>
#include <linux/smpboot.h>
+#include <linux/context_tracking.h>
#include <linux/tick.h>
#include <linux/irq.h>
+#include <linux/isolation.h>

#define CREATE_TRACE_POINTS
#include <trace/events/irq.h>
@@ -335,6 +337,11 @@ void irq_enter(void)
_local_bh_enable();
}

+ if (context_tracking_cpu_is_enabled() &&
+ context_tracking_in_user() &&
+ !in_interrupt())
+ task_isolation_debug(smp_processor_id());
+
__irq_enter();
}

--
2.1.2