[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>

3 files changed, 18 insertions, 8 deletions

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 498bfbd3b4e1..ea097dddc44f 100644
--- a/include/linux/lockdep.h
+++ b/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
 
 /*
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 69e92c6b0472..07a3d74a84be 100644
--- a/kernel/lockdep.c
+++ b/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
diff --git a/kernel/sched.c b/kernel/sched.c
index 8a0afb97af71..5cd833bc2173 100644
--- a/kernel/sched.c
+++ b/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