rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common()

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

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 550193a..2c17859 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -825,7 +825,7 @@ 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)) {