From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Rostedt Subject: [PATCH RT 1/6] rcutree/rcu_bh_qs: disable irq while calling rcu_preempt_qs() Date: Tue, 04 Mar 2014 19:33:34 -0500 Message-ID: <20140305003346.299958746@goodmis.org> References: <20140305003333.402759240@goodmis.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: Thomas Gleixner , Carsten Emde , Sebastian Andrzej Siewior , John Kacur , Paul Gortmaker , , Tiejun Chen , Bin Jiang To: linux-kernel@vger.kernel.org, linux-rt-users Return-path: Content-Disposition: inline; filename=0001-rcutree-rcu_bh_qs-disable-irq-while-calling-rcu_pree.patch Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org 3.2.55-rt79-rc1 stable review patch. If anyone has any objections, please let me know. ------------------ From: Tiejun Chen 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 Signed-off-by: Steven Rostedt --- kernel/rcutree.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 82c2224..6c2ec2d 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -175,7 +175,12 @@ 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) -- 1.8.5.3