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

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Message-ID: <20230217102521.GA27682@redhat.com>
Date:   Fri, 17 Feb 2023 11:25:21 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     David Vernet <void@...ifault.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 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.

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

Thanks,

Oleg.