From 0f1ac8fd254b6c3e77950a1c4ee67be5dc88f7e0 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Tue, 15 Jan 2013 22:11:19 -0500 Subject: tracing/lockdep: Disable lockdep first in entering NMI 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(-) (limited to 'include') diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h index 624ef3f45c8e..57bfdce8fb90 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 */ -- cgit v1.2.3