Date: Sun, 11 Dec 2005 20:38:09 -0800 (PST)
Message-Id: <20051211.203809.127057416.davem@davemloft.net>
To: akpm@osdl.org
Cc: paulmck@us.ibm.com, oleg@tv-sign.ru, vatsa@in.ibm.com,
       linux-kernel@vger.kernel.org, dipankar@in.ibm.com
Subject: Re: [PATCH] Fix RCU race in access of nohz_cpu_mask
From: "David S. Miller" <davem@davemloft.net>
In-Reply-To: <20051211203226.4deafd59.akpm@osdl.org>
References: <439B24A7.E2508AAE@tv-sign.ru>
	<20051212031053.GA8748@us.ibm.com>
	<20051211203226.4deafd59.akpm@osdl.org>
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 805
Lines: 21

From: Andrew Morton <akpm@osdl.org>
Date: Sun, 11 Dec 2005 20:32:26 -0800

> So foo_mb() in preemptible code is potentially buggy.
> 
> I guess we assume that a context switch accidentally did enough of the
> right types of barriers for things to work OK.

A trap ought to flush all memory operations.

There are some incredibly difficult memory error handling cases if the
cpu does not synchronize all pending memory operations when a trap
occurs.

Failing that, yes, to be absolutely safe we'd need to have some
explicit memory barrier in the context switch.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/