linux-kernel - Re: [PATCH v2 1/4] introduce for_each_thread() to replace the buggy while_each

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Message-ID: <alpine.DEB.2.02.1312051521540.7717@chino.kir.corp.google.com>
Date:	Thu, 5 Dec 2013 15:23:55 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mandeep Singh Baines <msb@...omium.org>,
	"Ma, Xindong" <xindong.ma@...el.com>,
	Michal Hocko <mhocko@...e.cz>,
	Sameer Nanda <snanda@...omium.org>,
	Sergey Dyasly <dserrg@...il.com>,
	"Tu, Xiaobing" <xiaobing.tu@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] introduce for_each_thread() to replace the buggy
 while_each_thread()

On Thu, 5 Dec 2013, Oleg Nesterov wrote:

> > Minor: should the definitions of thread_{head,node} be annotated with
> > __rcu for users of CONFIG_SPARSE_RCU_POINTER?
> 
> Perhaps. And perhaps task_struct->tasks. And perhaps we should add
> rcu_read_lock_held() || lockdep_is_held(tasklist) || lockdep_is_held(siglock)
> into for_each_process/thead.
> 
> But lets do this later. At least we should avoid the false positives.
> 

Ok, thanks.  I think anything we can do to catch these cases of 
unprotected usage even with some debugging options like 
CONFIG_SPARSE_RCU_POINTER and CONFIG_LOCKDEP will help given the number of 
places you found that were doing it incorrectly already.
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