From mboxrd@z Thu Jan  1 00:00:00 1970
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: Re: [v2 PATCH] rcutree/rcu_bh_qs: disable irq while calling
 rcu_preempt_qs()
Date: Fri, 20 Dec 2013 14:30:42 +0100
Message-ID: <20131220133042.GC10249@linutronix.de>
References: <1387360309-12801-1-git-send-email-tiejun.chen@windriver.com>
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To: Tiejun Chen <tiejun.chen@windriver.com>
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* Tiejun Chen | 2013-12-18 17:51:49 [+0800]:

>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.
>
>Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
>Signed-off-by: Bin Jiang <bin.jiang@windriver.com>
Applied.

Sebastian