[PATCH RT 6/8] sched: Better debug output for might sleep

Steven Rostedt
2012-10-12T01:23:06Z

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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.

Cc: stable-rt@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
include/linux/sched.h | 4 ++++
kernel/sched.c | 23 +++++++++++++++++++++--
2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 03498cc..12317b6 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1612,6 +1612,10 @@ struct task_struct {
int kmap_idx;
pte_t kmap_pte[KM_TYPE_NR];
#endif
+
+#ifdef CONFIG_DEBUG_PREEMPT
+ unsigned long preempt_disable_ip;
+#endif
};

#ifdef CONFIG_PREEMPT_RT_FULL
diff --git a/kernel/sched.c b/kernel/sched.c
index 87654e6..cdf9484 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4487,8 +4487,13 @@ void __kprobes add_preempt_count(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(add_preempt_count);

@@ -4530,6 +4535,13 @@ static noinline void __schedule_bug(struct task_struct *prev)
print_modules();
if (irqs_disabled())
print_irqtrace_events(prev);
+#ifdef DEBUG_PREEMPT
+ if (in_atomic_preempt_off()) {
+ pr_err("Preemption disabled at:");
+ print_ip_sym(current->preempt_disable_ip);
+ pr_cont("\n");
+ }
+#endif

if (regs)
show_regs(regs);
@@ -8912,6 +8924,13 @@ void __might_sleep(const char *file, int line, int preempt_offset)
debug_show_held_locks(current);
if (irqs_disabled())
print_irqtrace_events(current);
+#ifdef 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);
--
1.7.10.4