linux-kernel - Re: [RFC v2 0/6] Track RCU dereferences in RCU read-side critical sections

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Date:	Thu, 25 Feb 2016 15:32:43 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Boqun Feng <boqun.feng@...il.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>, sasha.levin@...cle.com
Subject: Re: [RFC v2 0/6] Track RCU dereferences in RCU read-side critical
 sections

On Tue, Feb 16, 2016 at 01:57:39PM +0800, Boqun Feng wrote:
> As a characteristic of RCU, read-side critical sections have a very
> loose connection with rcu_dereference()s, which is you can only be sure
> about an rcu_dereference() might be called in some read-side critical
> section, but if code gets complex, you may not be sure which read-side
> critical section exactly, this might be also an problem for some other
> locking mechanisms, that is the critical sections protecting data and
> the data accesses protected are not clearly correlated.
> 
> In this series, we are introducing LOCKED_ACCESS framework and based on
> which, we implement the RCU_LOCKED_ACCESS functionality to give us a
> clear hint: which rcu_dereference() happens in which RCU read-side
> critical section. 
> 
> After this series applied, and if CONFIG_RCU_LOCKED_ACCESS=y, the proc
> file /proc/locked_access/rcu will show all relationships collected so
> far for rcu_read_lock() and their friends and rcu_dereference*().
> 

But why !? What does this bring us, why do I want to even look at these
patches?