linux-kernel - Re: [PATCH v2 4/9] cgroup: rstat: add WARN_ON

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Message-ID: <CAJD7tkbjmBaXghQ+14Hy28r2LoWSim+LEjOPxaamYeA_kr2uVw@mail.gmail.com>
Date:   Thu, 30 Mar 2023 01:19:29 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>, Tejun Heo <tj@...nel.org>,
        Josef Bacik <josef@...icpanda.com>,
        Jens Axboe <axboe@...nel.dk>,
        Zefan Li <lizefan.x@...edance.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Koutný <mkoutny@...e.com>,
        Vasily Averin <vasily.averin@...ux.dev>,
        cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH v2 4/9] cgroup: rstat: add WARN_ON_ONCE() if flushing
 outside task context

On Thu, Mar 30, 2023 at 1:15 AM Michal Hocko <mhocko@...e.com> wrote:
>
> On Thu 30-03-23 01:06:26, Yosry Ahmed wrote:
> [...]
> > If we achieve that, do you think it makes sense to add
> > WARN_ON_ONCE(irqs_disabled()) instead to prevent future users from
> > flushing while disabling irqs or in irq context?
>
> WARN_ON (similar to BUG_ON) will not prevent anybody from doing bad
> things. We already have means to shout about sleepable code being
> invoked from an atomic context and there is no reason to duplicate that.
> As I've said earlier WARN_ON might panic the system in some
> configurations (and yes they are used also in production systems - do
> not ask me why...). So please be careful about that and use that only
> when something really bad (yet recoverable) is going on.

Thanks for the information (I was about to ask why about production
systems, but okay..). I will avoid WARN_ON completely. For the
purposes of this series I will drop this patch anyway.

Any idea how to shout about "hey this may take too long, why are you
doing it with irqs disabled?!"?

>
> --
> Michal Hocko
> SUSE Labs