When debug preempt is enabled, preempt_disable() can be traced by function and function graph tracing.
There's a place in the function graph tracer that calls trace_clock() which eventually calls cycles_2_ns() outside of the recursion protection. When cycles_2_ns() calls preempt_disable() it gets traced and the graph tracer will go into a recursive loop causing a crash or worse, a triple fault. Simple fix is to use preempt_disable_notrace() in cycles_2_ns, which makes sense because the preempt_disable() tracing may use that code too, and it tracing it, even with recursion protection is rather pointless. Signed-off-by: Steven Rostedt <[email protected]> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 19e5adb..acb3b60 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -209,7 +209,7 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc) * dance when its actually needed. */ - preempt_disable(); + preempt_disable_notrace(); data = this_cpu_read(cyc2ns.head); tail = this_cpu_read(cyc2ns.tail); @@ -229,7 +229,7 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc) if (!--data->__count) this_cpu_write(cyc2ns.tail, data); } - preempt_enable(); + preempt_enable_notrace(); return ns; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
