linux-kernel - Re: Can srcu_read_lock() be called from interrupt context?

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Message-ID: <20151103095539.GD29027@linux.vnet.ibm.com>
Date:	Tue, 3 Nov 2015 01:55:39 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Yunhong Jiang <yunhong.jiang@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org, jiangshanlai@...il.com
Subject: Re: Can srcu_read_lock() be called from interrupt context?

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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