From 22775b1bef957df737c1ed9fe020cacc3613ec78 Mon Sep 17 00:00:00 2001 From: Tiejun Chen Date: Wed, 18 Dec 2013 17:51:49 +0800 Subject: [PATCH] rcutree/rcu_bh_qs: disable irq while calling rcu_preempt_qs() Any callers to the function rcu_preempt_qs() must disable irqs in order to protect the assignment to ->rcu_read_unlock_special. In RT case, rcu_bh_qs() as the wrapper of rcu_preempt_qs() is called in some scenarios where irq is enabled, like this path, do_single_softirq() | + local_irq_enable(); + handle_softirq() | | | + rcu_bh_qs() | | | + rcu_preempt_qs() | + local_irq_disable() So here we'd better disable irq directly inside of rcu_bh_qs() to fix this, otherwise the kernel may be freezable sometimes as observed. And especially this way is also kind and safe for the potential rcu_bh_qs() usage elsewhere in the future. Cc: stable-rt@vger.kernel.org Signed-off-by: Tiejun Chen Signed-off-by: Bin Jiang Signed-off-by: Sebastian Andrzej Siewior --- kernel/rcu/tree.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 967546cca4a6..f3710e78a2b6 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -204,7 +204,12 @@ static void rcu_preempt_qs(int cpu); void rcu_bh_qs(int cpu) { + unsigned long flags; + + /* Callers to this function, rcu_preempt_qs(), must disable irqs. */ + local_irq_save(flags); rcu_preempt_qs(cpu); + local_irq_restore(flags); } #else void rcu_bh_qs(int cpu)