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Subject[patch] lockdep: print irq-trace info on asserts
Subject: [patch] lockdep: print irq-trace info on asserts
From: Ingo Molnar <mingo@elte.hu>

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>
---
include/linux/lockdep.h | 16 +++++++++++++---
kernel/lockdep.c | 6 +-----
kernel/sched.c | 4 ++++
3 files changed, 18 insertions(+), 8 deletions(-)

Index: linux/include/linux/lockdep.h
===================================================================
--- linux.orig/include/linux/lockdep.h
+++ linux/include/linux/lockdep.h
@@ -282,15 +282,25 @@ 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

/*
Index: linux/kernel/lockdep.c
===================================================================
--- linux.orig/kernel/lockdep.c
+++ linux/kernel/lockdep.c
@@ -1449,7 +1449,7 @@ check_usage_backwards(struct task_struct
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);
@@ -1462,10 +1462,6 @@ static inline void print_irqtrace_events
print_ip_sym(curr->softirq_disable_ip);
}

-#else
-static inline void print_irqtrace_events(struct task_struct *curr)
-{
-}
#endif

static int
Index: linux/kernel/sched.c
===================================================================
--- linux.orig/kernel/sched.c
+++ linux/kernel/sched.c
@@ -3353,6 +3353,8 @@ 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));
@@ -6895,6 +6897,8 @@ 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
-
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