Date: Tue, 3 Nov 2015 01:55:39 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Yunhong Jiang <yunhong.jiang@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, jiangshanlai@gmail.com
Subject: Re: Can srcu_read_lock() be called from interrupt context?
Message-ID: <20151103095539.GD29027@linux.vnet.ibm.com>
Reply-To: paulmck@linux.vnet.ibm.com
References: <20151103015656.GA10358@jnakajim-build>
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On Mon, Nov 02, 2015 at 05:56:56PM -0800, Yunhong Jiang wrote:
> Hi, Paul
> 	I have a question to the srcu_read_lock(). Can it be invoked on 
> interrupt context? According to 
> http://lxr.free-electrons.com/source/kernel/rcu/srcu.c#L292 it can only be 
> called from process context, but according to 
> http://lxr.free-electrons.com/source/include/linux/srcu.h#L213 seems it's ok 
> from irq context only if it matches with the srcu_read_unlock. Can you 
> please give some hints?

Adding Lai Jianshan for his thoughts.

I believe that srcu.h is correct, at least assuming that interrupts do
not nest too deeply.  (If they were to nest four billion deep, then the
->seq[] counter could overflow, defeating the checks, but the CPU stack
would have overflowed long before.)

Lai, am I missing anything here?

							Thanx, Paul

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