On Fri, Feb 21, 2020 at 02:34:24PM +0100, Peter Zijlstra wrote: > From: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> > > It's confusing that rcu_nmi_enter() is marked NOKPROBE and > rcu_nmi_exit() is not. One may think that the exit needs to be marked > for the same reason the enter is, as rcu_nmi_exit() reverts the RCU > state back to what it was before rcu_nmi_enter(). But the reason has > nothing to do with the state of RCU. > > The breakpoint handler (int3 on x86) must not have any kprobe on it > until the kprobe handler is called. Otherwise, it can cause an infinite > recursion and crash the machine. It just so happens that > rcu_nmi_enter() is called by the int3 handler before the kprobe handler > can run, and therefore needs to be marked as NOKPROBE. > > Comment this to remove the confusion to why rcu_nmi_enter() is marked > NOKPROBE but rcu_nmi_exit() is not. > > Reported-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > Reviewed-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx> > Acked-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > Link: https://lore.kernel.org/r/20200213163800.5c51a5f1@xxxxxxxxxxxxxxxxxx Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
