sched: Add better debug output for might_sleep()

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>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1391803122-4425-4-git-send-email-bigeasy@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index c49a2585ff7d334e45328a90d6f8bdc716a9be2a..825ed838d4b967d91242fcdc3f06e932d7582499 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1463,6 +1463,9 @@ 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 a01fe6cfdb9b6935e4495512a843714d7ebe9498..c94e851dc98176438778040fa7ae661f903efbe1 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2501,8 +2501,13 @@ 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);
 
@@ -2545,6 +2550,13 @@ 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);
 }
@@ -6946,6 +6958,13 @@ 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);