linux-kernel - Re: [Stable-review] [07/55] SUNRPC: Fix a race between work-queue and rpc_killall

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Date:	Sun, 07 Aug 2011 18:38:01 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Greg KH <gregkh@...e.de>
Cc:	linux-kernel@...r.kernel.org, stable@...nel.org,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	stable-review@...nel.org, alan@...rguk.ukuu.org.uk
Subject: Re: [Stable-review] [07/55] SUNRPC: Fix a race between work-queue
 and rpc_killall_tasks

On Fri, 2011-08-05 at 17:01 -0700, Greg KH wrote:
> 2.6.32-longterm review patch.  If anyone has any objections, please let us know.
> 
> ------------------
> 
> From: Trond Myklebust <Trond.Myklebust@...app.com>
> 
> commit b55c59892e1f3b6c7d4b9ccffb4263e1486fb990 upstream.
> 
> Since rpc_killall_tasks may modify the rpc_task's tk_action field
> without any locking, we need to be careful when dereferencing it.
[...]

This isn't nearly careful enough to avoid races.  You must at least use
the ACCESS_ONCE macro, otherwise the compiler can just optimise away the
local variable this introduces.

Ben.


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