linux-kernel - Re: [PATCH] mm/mempolicy: fix sleeping function called from invalid context

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 9 Jun 2014 02:13:57 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Gu Zheng <guz.fnst@...fujitsu.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>, linux-mm@...ck.org,
	Cgroups <cgroups@...r.kernel.org>, stable@...r.kernel.org,
	Li Zefan <lizefan@...wei.com>
Subject: Re: [PATCH] mm/mempolicy: fix sleeping function called from invalid
 context

On Mon, 9 Jun 2014, Gu Zheng wrote:

> > I think your patch addresses the problem that you're reporting but misses 
> > the larger problem with cpuset.mems rebinding on fork().  When the 
> > forker's task_struct is duplicated (which includes ->mems_allowed) and it 
> > races with an update to cpuset_being_rebound in update_tasks_nodemask() 
> > then the task's mems_allowed doesn't get updated.
> 
> Yes, you are right, this patch just wants to address the bug reported above.
> The race condition you mentioned above inherently exists there, but it is yet
> another issue, the rcu lock here makes no sense to it, and I think we need
> additional sync-mechanisms if want to fix it.

Yes, the rcu lock is not providing protection for any critical section 
here that requires (1) the forker's cpuset to be stored in 
cpuset_being_rebound or (2) the forked thread's cpuset to be rebound by 
the cpuset nodemask update, and no race involving the two.

> But thinking more, though the current implementation has flaw, but I worry
> about the negative effect if we really want to fix it. Or maybe the fear
> is unnecessary.:) 
> 

It needs to be slightly rewritten to work properly without negatively 
impacting the latency of fork().  Do you have the cycles to do it?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/