On Tue, 4 Feb 2014, Steven Rostedt wrote: > 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]>
Acked-by-me > 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/
