On Fri, 12 May 2017 11:50:03 -0700 "Paul E. McKenney" <[email protected]> wrote:
> On Fri, May 12, 2017 at 02:36:19PM -0400, Steven Rostedt wrote: > > On Fri, 12 May 2017 11:25:35 -0700 > > "Paul E. McKenney" <[email protected]> wrote: > > > > > On Fri, May 12, 2017 at 01:15:45PM -0400, Steven Rostedt wrote: > > > > From: "Steven Rostedt (VMware)" <[email protected]> > > > > > > > > As stack tracing now requires "rcu watching", force RCU to be watching > > > > when > > > > recording a stack trace. > > > > > > > > Signed-off-by: Steven Rostedt (VMware) <[email protected]> > > > > > > Assuming that you never get to __trace_stack() if in an NMI handler, > > > this looks good to me! > > > > > > In contrast, if if __trace_stack() ever is called from an NMI handler, > > > invoking rcu_irq_enter() can be fatal. > > > > Then someone may die. > > > > OK, what's the case of running this in nmi? How does perf do it? > > I have no idea. If it cannot happen, then it cannot happen and all > is well, RCU is happy, and I am happy. ;-) > > > Do we just skip the check if it is in an nmi? > > > > if (!in_nmi()) { > > if (unlikely(rcu_irq_enter_disabled())) > > return; > > rcu_irq_enter(); > > } > > > > __ftrace_trace_stack(); > > > > if (!in_nmi()) > > rcu_irq_exit(); > > > > ? > > If it -can- happen, bail out of the function without doing the Why? > __ftrace_trace_stack()? Or does that just cause other problems further > down the road? Or BUG_ON(in_nmi())? Why? > > But again if it cannot happen, no problem and no need for extra code. > We can't call stack trace from nmi anymore? It calls rcu_read_lock() which is why we need to make sure rcu is watching, otherwise lockdep complains. -- Steve
