linux-kernel - Using RCU with rcu_read

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Message-ID: <d120d5000706151200u34bd6728n7fca0983d6175f29@mail.gmail.com>
Date:	Fri, 15 Jun 2007 15:00:46 -0400
From:	"Dmitry Torokhov" <dmitry.torokhov@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Using RCU with rcu_read_lock()?

Hi,

I have a piece of code that is always called under a spinlock with
interrups disabled. Within that piece of code I iterate through a
list. I have another piece of code that wants to modify that list. I
have 2 options:

1) Have the other piece of code acquire the same spinlock
2) Use RCU

I don't want to do 1) because the otheir piece of code does not really
care about object owning the spinlock and so acquiring the spinlock is
"not nice". However it is guaranteed that the piece of code that
accesses lock runs atomically with interrupts disabled. So
rcu_read_lock() would be superfluos there.

Is it possible to still use list_for_each_rcu() and friends to access
that list without rcu_read_lock()? Or it is betteruse complete RCU
interface and eat cost of couple of extra instrctions?

-- 
Dmitry
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