linux-kernel - Re: Udpated sys_membarrier() speedup patch, FYI

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Message-ID: <20170731083746.mggdh7pcdycjte2c@hirez.programming.kicks-ass.net>
Date:   Mon, 31 Jul 2017 10:37:46 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Avi Kivity <avi@...lladb.com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        maged michael <maged.michael@...il.com>,
        Andrew Hunter <ahh@...gle.com>, gromer <gromer@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Udpated sys_membarrier() speedup patch, FYI

On Mon, Jul 31, 2017 at 09:03:09AM +0300, Avi Kivity wrote:
> I remembered that current->mm does not change when switching to a kernel
> task, but my Kernlish is very rusty, or maybe it has changed.

kernel threads do indeed preserve the mm of the old userspace task, but
we track that in ->active_mm. Their ->mm will be NULL.