The following commit has been merged into the core/urgent branch of tip:

Commit-ID: bf37da98c51825c90432d340e135cced37a7460d Gitweb: https://git.kernel.org/tip/bf37da98c51825c90432d340e135cced37a7460d Author: Paul E. McKenney paulmck@kernel.org AuthorDate: Thu, 12 Mar 2020 16:55:07 -07:00 Committer: Paul E. McKenney paulmck@kernel.org CommitterDate: Sun, 05 Apr 2020 14:22:15 -07:00

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 --- 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 550193a..2c17859 100644 --- 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)) {