From: Peter Zijlstra peterz@infradead.org
[ Upstream commit 6dbce04d8417ae706596366e16841d77c454ba52 ]
Eugenio managed to tickle #PF from NMI context which resulted in hitting a WARN in RCU through irqentry_enter() -> __rcu_irq_enter_check_tick().
However, this situation is perfectly sane and does not warrant an WARN. The #PF will (necessarily) be atomic and not require messing with the tick state, so early return is correct. This commit therefore removes the WARN.
Fixes: aaf2bc50df1f ("rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter()") Reported-by: "Eugenio Pérez" eupm90@gmail.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Andy Lutomirski luto@kernel.org Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/rcu/tree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index bd04b09b84b32..655ade095e043 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -928,8 +928,8 @@ void __rcu_irq_enter_check_tick(void) { struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
- // Enabling the tick is unsafe in NMI handlers. - if (WARN_ON_ONCE(in_nmi())) + // If we're here from NMI there's nothing to do. + if (in_nmi()) return;
RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),