| From | Greg Kroah-Hartman <> | Subject | [PATCH 5.6 64/71] rcu: Dont acquire lock in NMI handler in rcu_nmi_enter_common() | Date | Mon, 20 Apr 2020 14:39:18 +0200 |
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From: Paul E. McKenney <paulmck@kernel.org>
commit bf37da98c51825c90432d340e135cced37a7460d upstream.
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 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -816,7 +816,7 @@ static __always_inline void rcu_nmi_ente 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) && !rdp->rcu_forced_tick) { raw_spin_lock_rcu_node(rdp->mynode);
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