linux-kernel - Re: [RFC PATCH 2/3] sched: membarrier: cover kthread_use

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Message-ID: <833020242.9878.1597611922236.JavaMail.zimbra@efficios.com>
Date:   Sun, 16 Aug 2020 17:05:22 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Will Deacon <will@...nel.org>, paulmck <paulmck@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Nicholas Piggin <npiggin@...il.com>
Subject: Re: [RFC PATCH 2/3] sched: membarrier: cover kthread_use_mm (v2)

----- On Aug 16, 2020, at 3:09 AM, Hillf Danton hdanton@...a.com wrote:

> On Fri, 14 Aug 2020 12:43:57 -0400 Mathieu Desnoyers wrote:
>> 
>> Given that no prior kthread use this guarantee and that it only affects
>> kthreads, adding this guarantee does not affect user-space ABI.
> 
> Can you expand a bit on why kthreads like ksoftirqd have to ack the
> IPIs from Dave who's not CAP_SYS_ADMIN.

Do ksoftirqd kthreads ever use kthread_use_mm() to access user
processes' memory ? If not, then they won't be disturbed by any IPI.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com