Messages in this thread Patch in this message | | | Date | Sun, 13 Dec 2020 19:01:03 -0000 | From | "tip-bot2 for Peter Zijlstra" <> | Subject | [tip: core/rcu] rcu: Allow rcu_irq_enter_check_tick() from NMI |
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The following commit has been merged into the core/rcu branch of tip:
Commit-ID: 6dbce04d8417ae706596366e16841d77c454ba52 Gitweb: https://git.kernel.org/tip/6dbce04d8417ae706596366e16841d77c454ba52 Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Mon, 16 Nov 2020 13:10:12 +01:00 Committer: Paul E. McKenney <paulmck@kernel.org> CommitterDate: Thu, 19 Nov 2020 19:34:17 -08:00
rcu: Allow rcu_irq_enter_check_tick() from NMI
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> --- 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 06895ef..93e1808 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(),
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