| From | paulmck@kernel ... | Subject | [PATCH v4 tip/core/rcu 38/38] rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common() | Date | Wed, 15 Apr 2020 11:19:41 -0700 |
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From: "Paul E. McKenney" <paulmck@kernel.org>
The rcu_nmi_enter_common() function can be invoked both in interrupt and NMI handlers. If it is invoked from process context (as opposed to userspace or idle context) on a nohz_full CPU, it might acquire the CPU's leaf rcu_node structure's ->lock. Because this lock is held only with interrupts disabled, this is safe from an interrupt handler, but doing so from an NMI handler can result in self-deadlock.
This commit therefore adds "irq" to the "if" condition so as to only acquire the ->lock from irq handlers or process context, never from an NMI handler.
Fixes: 5b14557b073c ("rcu: Avoid tick_dep_set_cpu() misordering") Reported-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> Cc: <stable@vger.kernel.org> # 5.5.x --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 7dd7a17..573fd78 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -876,7 +876,7 @@ static __always_inline void rcu_nmi_enter_common(bool irq) rcu_cleanup_after_idle(); incby = 1; - } else if (tick_nohz_full_cpu(rdp->cpu) && + } else if (irq && tick_nohz_full_cpu(rdp->cpu) && rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE && READ_ONCE(rdp->rcu_urgent_qs) && !READ_ONCE(rdp->rcu_forced_tick)) { -- 2.9.5
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