[PATCH] lockdep: print irq-trace info on asserts

When we print an assert due to scheduling-in-atomic bugs, and if lockdep
is enabled, then the IRQ tracing information of lockdep can be printed
to pinpoint the code location that disabled interrupts. This saved me
quite a bit of debugging time in cases where the backtrace did not
identify the irq-disabling site well enough.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/lockdep.h

@@ -281,15 +281,25 @@ struct lock_class_key { };
 #if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_GENERIC_HARDIRQS)
 extern void early_init_irq_lock_class(void);
 #else
-# define early_init_irq_lock_class()		do { } while (0)
+static inline void early_init_irq_lock_class(void)
+{
+}
 #endif
 
 #ifdef CONFIG_TRACE_IRQFLAGS
 extern void early_boot_irqs_off(void);
 extern void early_boot_irqs_on(void);
+extern void print_irqtrace_events(struct task_struct *curr);
 #else
-# define early_boot_irqs_off()			do { } while (0)
-# define early_boot_irqs_on()			do { } while (0)
+static inline void early_boot_irqs_off(void)
+{
+}
+static inline void early_boot_irqs_on(void)
+{
+}
+static inline void print_irqtrace_events(struct task_struct *curr)
+{
+}
 #endif
 
 /*

kernel/lockdep.c

@@ -1447,7 +1447,7 @@ check_usage_backwards(struct task_struct *curr, struct held_lock *this,
 	return print_irq_inversion_bug(curr, backwards_match, this, 0, irqclass);
 }
 
-static inline void print_irqtrace_events(struct task_struct *curr)
+void print_irqtrace_events(struct task_struct *curr)
 {
 	printk("irq event stamp: %u\n", curr->irq_events);
 	printk("hardirqs last  enabled at (%u): ", curr->hardirq_enable_event);
@@ -1460,10 +1460,6 @@ static inline void print_irqtrace_events(struct task_struct *curr)
 	print_ip_sym(curr->softirq_disable_ip);
 }
 
-#else
-static inline void print_irqtrace_events(struct task_struct *curr)
-{
-}
 #endif
 
 static int

kernel/sched.c

@@ -3429,6 +3429,8 @@ asmlinkage void __sched schedule(void)
 			"%s/0x%08x/%d\n",
 			current->comm, preempt_count(), current->pid);
 		debug_show_held_locks(current);
+		if (irqs_disabled())
+			print_irqtrace_events(current);
 		dump_stack();
 	}
 	profile_hit(SCHED_PROFILING, __builtin_return_address(0));
@@ -6977,6 +6979,8 @@ void __might_sleep(char *file, int line)
 		printk("in_atomic():%d, irqs_disabled():%d\n",
 			in_atomic(), irqs_disabled());
 		debug_show_held_locks(current);
+		if (irqs_disabled())
+			print_irqtrace_events(current);
 		dump_stack();
 	}
 #endif