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Subject[PATCH 3/6] sched: Better debug output for might sleep
Date
From: Thomas Gleixner <tglx@linutronix.de>

might sleep can tell us where interrupts have been disabled, but we
have no idea what disabled preemption. Add some debug infrastructure.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
include/linux/sched.h | 3 +++
kernel/sched/core.c | 23 +++++++++++++++++++++--
2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 68a0e84..0e2fb59 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1459,6 +1459,9 @@ struct task_struct {
struct mutex perf_event_mutex;
struct list_head perf_event_list;
#endif
+#ifdef CONFIG_DEBUG_PREEMPT
+ unsigned long preempt_disable_ip;
+#endif
#ifdef CONFIG_NUMA
struct mempolicy *mempolicy; /* Protected by alloc_lock */
short il_next;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fbaec2a..3112b28 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2510,8 +2510,13 @@ void __kprobes preempt_count_add(int val)
DEBUG_LOCKS_WARN_ON((preempt_count() & PREEMPT_MASK) >=
PREEMPT_MASK - 10);
#endif
- if (preempt_count() == val)
- trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
+ if (preempt_count() == val) {
+ unsigned long ip = get_parent_ip(CALLER_ADDR1);
+#ifdef CONFIG_DEBUG_PREEMPT
+ current->preempt_disable_ip = ip;
+#endif
+ trace_preempt_off(CALLER_ADDR0, ip);
+ }
}
EXPORT_SYMBOL(preempt_count_add);

@@ -2554,6 +2559,13 @@ static noinline void __schedule_bug(struct task_struct *prev)
print_modules();
if (irqs_disabled())
print_irqtrace_events(prev);
+#ifdef CONFIG_DEBUG_PREEMPT
+ if (in_atomic_preempt_off()) {
+ pr_err("Preemption disabled at:");
+ print_ip_sym(current->preempt_disable_ip);
+ pr_cont("\n");
+ }
+#endif
dump_stack();
add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}
@@ -6957,6 +6969,13 @@ void __might_sleep(const char *file, int line, int preempt_offset)
debug_show_held_locks(current);
if (irqs_disabled())
print_irqtrace_events(current);
+#ifdef CONFIG_DEBUG_PREEMPT
+ if (!preempt_count_equals(preempt_offset)) {
+ pr_err("Preemption disabled at:");
+ print_ip_sym(current->preempt_disable_ip);
+ pr_cont("\n");
+ }
+#endif
dump_stack();
}
EXPORT_SYMBOL(__might_sleep);
--
1.9.rc1


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