Messages in this thread | | | Date | Thu, 6 Apr 2017 11:12:22 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 3/4] tracing: Add stack_tracer_disable/enable() functions |
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On Thu, Apr 06, 2017 at 12:42:40PM -0400, Steven Rostedt wrote: > From: "Steven Rostedt (VMware)" <rostedt@goodmis.org> > > There are certain parts of the kernel that can not let stack tracing > proceed (namely in RCU), because the stack tracer uses RCU, and parts of RCU > internals can not handle having RCU read side locks taken. > > Add stack_tracer_disable() and stack_tracer_enable() functions to let RCU > stop stack tracing on the current CPU as it is in those critical sections.
s/as it is in/when it is in/?
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
One quibble above, one objection below.
Thanx, Paul
> --- > include/linux/ftrace.h | 6 ++++++ > kernel/trace/trace_stack.c | 28 ++++++++++++++++++++++++++++ > 2 files changed, 34 insertions(+) > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > index ef7123219f14..40afee35565a 100644 > --- a/include/linux/ftrace.h > +++ b/include/linux/ftrace.h > @@ -286,6 +286,12 @@ int > stack_trace_sysctl(struct ctl_table *table, int write, > void __user *buffer, size_t *lenp, > loff_t *ppos); > + > +void stack_tracer_disable(void); > +void stack_tracer_enable(void); > +#else > +static inline void stack_tracer_disable(void) { } > +static inline void stack_tracer_enabe(void) { } > #endif > > struct ftrace_func_command { > diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c > index 05ad2b86461e..5adbb73ec2ec 100644 > --- a/kernel/trace/trace_stack.c > +++ b/kernel/trace/trace_stack.c > @@ -41,6 +41,34 @@ static DEFINE_MUTEX(stack_sysctl_mutex); > int stack_tracer_enabled; > static int last_stack_tracer_enabled; > > +/** > + * stack_tracer_disable - temporarily disable the stack tracer > + * > + * There's a few locations (namely in RCU) where stack tracing > + * can not be executed. This function is used to disable stack > + * tracing during those critical sections. > + * > + * This function will disable preemption. stack_tracer_enable() > + * must be called shortly after this is called. > + */ > +void stack_tracer_disable(void) > +{ > + preempt_disable_notrace();
Interrupts are disabled in all current call points, so you don't really need to disable preemption. I would normally not worry, given the ease-of-use improvements, but some people get annoyed about even slight increases in idle-entry overhead.
> + this_cpu_inc(trace_active); > +} > + > +/** > + * stack_tracer_enable - re-enable the stack tracer > + * > + * After stack_tracer_disable() is called, stack_tracer_enable() > + * must shortly be called afterward. > + */ > +void stack_tracer_enable(void) > +{ > + this_cpu_dec(trace_active); > + preempt_enable_notrace();
Ditto...
> +} > + > void stack_trace_print(void) > { > long i; > -- > 2.10.2 > >
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