Messages in this thread Patch in this message | | | Date | Mon, 16 Nov 2020 13:10:12 +0100 | From | Peter Zijlstra <> | Subject | [PATCH] rcu: Allow rcu_irq_enter_check_tick() from NMI |
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Any which way around; here's a proper patch...
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Subject: rcu: Allow rcu_irq_enter_check_tick() from NMI From: Peter Zijlstra <peterz@infradead.org> Date: Mon Nov 16 12:54:56 CET 2020
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.
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> Reviewed-by: Paul E. McKenney <paulmck@kernel.org> --- kernel/rcu/tree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- 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(),
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