linux-kernel - Re: [RFC PATCH] rcu: Add sparse check for RCU_INIT

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Date:	Thu, 25 Sep 2014 14:39:00 -0400
From:	Pranith Kumar <bobby.prani@...il.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	"open list:READ-COPY UPDATE..." <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] rcu: Add sparse check for RCU_INIT_POINTER()

On Thu, Sep 25, 2014 at 2:10 PM,  <josh@...htriplett.org> wrote:
> On Thu, Sep 25, 2014 at 02:03:34PM -0400, Pranith Kumar wrote:
>> Add a sparse check when RCU_INIT_POINTER() is used to assign a non __rcu
>> annotated pointer.
>>
>> Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
>
> Have you checked if this introduces a significant number of new warnings
> in the kernel?
>
> If not:
> Reviewed-by: Josh Triplett <josh@...htriplett.org>
>


I tested the above patch on a small test case where we are assigning
to a non __rcu annotated pointer and sparse does warn in that case.

I tried doing that and there were too many address space warnings
(maybe?) not related to __rcu annotation.

May be a diff of previous warnings and later warnings should show up
if any new warnings are being generated...

diff before.log after.log

> drivers/md/dm.c:2239:9: error: incompatible types in comparison expression (different address spaces)

Looking at this it shows that RCU_INIT_POINTER() is being used on a
non __rcu pointer. I will send in a patch fixing that.

Thanks!
-- 
Pranith
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