linux-kernel - Re: [PATCH] net/core: Use RCU_INIT

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Message-ID: <1395666875.12610.21.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 24 Mar 2014 06:14:35 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	Monam Agarwal <monamagarwal123@...il.com>, davem@...emloft.net,
	ebiederm@...ssion.com, cwang@...pensource.com, kaber@...sh.net,
	antonio@...hcoding.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net/core: Use RCU_INIT_POINTER(x, NULL) in netpoll.c

On Mon, 2014-03-24 at 07:11 -0400, Neil Horman wrote:
> On Mon, Mar 24, 2014 at 12:42:46AM +0530, Monam Agarwal wrote:
> > This patch replaces rcu_assign_pointer(x, NULL) with RCU_INIT_POINTER(x, NULL)
> > 
> > The rcu_assign_pointer() ensures that the initialization of a structure       
> > is carried out before storing a pointer to that structure. 
> > And in the case of the NULL pointer, there is no structure to initialize. 
> > So, rcu_assign_pointer(p, NULL) can be safely converted to RCU_INIT_POINTER(p, NULL)
> > 
> > Signed-off-by: Monam Agarwal <monamagarwal123@...il.com>
> No, I don't think this is right. __netpoll_cleanup can be called in parallel
> with bottom half access to dev->npinfo.  rcu_assign pointer is safe against
> those accesses, but RCU_INIT_POINTER is not.

Wow, it is always safe for NULL value.


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