From: Steven Rostedt When function tracing with either debug locks enabled or tracing preempt disabled, the add_preempt_count() is traced. This is an issue with lockdep and function tracing. As function tracing can disable interrupts, and lockdep records that change, lockdep may not be able to handle this recursion if it happens from an NMI context. The first thing that an NMI does is: #define nmi_enter() \ do { \ ftrace_nmi_enter(); \ BUG_ON(in_nmi()); \ add_preempt_count(NMI_OFFSET + HARDIRQ_OFFSET); \ lockdep_off(); \ rcu_nmi_enter(); \ trace_hardirq_enter(); \ } while (0) When the add_preempt_count() is traced, and the tracing callback disables interrupts, it will jump into the lockdep code. There's some places in lockdep that can't handle this re-entrance, and causes lockdep to fail. As the lockdep_off() (and lockdep_on) is a simple: void lockdep_off(void) { current->lockdep_recursion++; } and is never traced, it can be called first in nmi_enter() and lockdep_on() last in nmi_exit(). Cc: Peter Zijlstra Signed-off-by: Steven Rostedt --- include/linux/hardirq.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h index 624ef3f..57bfdce 100644 --- a/include/linux/hardirq.h +++ b/include/linux/hardirq.h @@ -180,10 +180,10 @@ extern void irq_exit(void); #define nmi_enter() \ do { \ + lockdep_off(); \ ftrace_nmi_enter(); \ BUG_ON(in_nmi()); \ add_preempt_count(NMI_OFFSET + HARDIRQ_OFFSET); \ - lockdep_off(); \ rcu_nmi_enter(); \ trace_hardirq_enter(); \ } while (0) @@ -192,10 +192,10 @@ extern void irq_exit(void); do { \ trace_hardirq_exit(); \ rcu_nmi_exit(); \ - lockdep_on(); \ BUG_ON(!in_nmi()); \ sub_preempt_count(NMI_OFFSET + HARDIRQ_OFFSET); \ ftrace_nmi_exit(); \ + lockdep_on(); \ } while (0) #endif /* LINUX_HARDIRQ_H */ -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/