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Subject[PATCH RT 05/14] rcutree/rcu_bh_qs: disable irq while calling rcu_preempt_qs()
3.10.32-rt31-rc2 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Tiejun Chen <tiejun.chen@windriver.com>

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 <tiejun.chen@windriver.com>
Signed-off-by: Bin Jiang <bin.jiang@windriver.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/rcutree.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 75743cb..5439cee 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -187,7 +187,12 @@ 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



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