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[v4,tip/core/rcu,38/38] rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common()

Message ID 20200415181941.11653-38-paulmck@kernel.org
State New
Headers show
Series None | expand

Commit Message

Paul E. McKenney April 15, 2020, 6:19 p.m. UTC 
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(-)
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Patch

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)) {