linux-kernel - Re: [PATCH] tasks: Extract rcu

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Date:   Mon, 27 Feb 2023 10:11:42 -0600
From:   David Vernet <void@...ifault.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com, kernel-team@...a.com,
        torvalds@...ux-foundation.org, ebiederm@...ssion.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tasks: Extract rcu_users out of union

On Fri, Feb 17, 2023 at 11:25:21AM +0100, Oleg Nesterov wrote:
> On 02/16, David Vernet wrote:
> >
> > On Thu, Feb 16, 2023 at 09:04:59AM +0100, Oleg Nesterov wrote:
> > >
> > > >    a task that's successfully looked
> > > >    up in e.g. the pid_list with find_task_by_pid_ns(), can always have a
> > > >    'usage' reference acquired on them, as it's guaranteed to be >
> > > >    0 until after the next gp.
> > >
> > > Yes. So it seems you need another key-to-task_struct map with rcu-safe
> > > lookup/get and thus the add() method needs inc_not_zero(task->rcu_users) ?
> >
> > Yes, exactly.
> 
> OK, in this case I agree, inc_not_zero(rcu_users) makes sense and thus we need
> this patch.

Thanks again for taking a look.

> 
> Just I was confused by the previous part of the changelog due to my bad English.

No worries at all -- the commit summary definitely could have been more
clear.

Does anyone else have any thoughts? Is there anything else we need to do
for this patch to land?

Thanks,
David