Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <ZCU1Bp+5bKNJzWIu@dhcp22.suse.cz> <CAJD7tka0CmRvcvB0k8DZuid1vC9OK_mFriHHbXNTUkVE7OjaTA@mail.gmail.com>
 <ZCU+8lSi+e4WgT3F@dhcp22.suse.cz> <CAJD7tkaKd9Bcb2-e83Q-kzF7G+crr1U+7uqUPBARXWq-LpyKvw@mail.gmail.com>
 <ZCVFA78lDj2/Uy0C@dhcp22.suse.cz> <CAJD7tkbjmBaXghQ+14Hy28r2LoWSim+LEjOPxaamYeA_kr2uVw@mail.gmail.com>
 <ZCVKqN2nDkkQFvO0@dhcp22.suse.cz> <CAJD7tkYEOVRcXs-Ag3mWn69EwE4rjFt9j5MAcTGCNE8BuhTd+A@mail.gmail.com>
 <ZCa9sixp3GJcjf8Y@dhcp22.suse.cz> <CAJD7tka-2vNn25=NdrKQoMf4ntdbWtojY0k4eAa-c9D+v7J=HQ@mail.gmail.com>
 <ZCqQfuprGreGYwFA@dhcp22.suse.cz>
In-Reply-To: <ZCqQfuprGreGYwFA@dhcp22.suse.cz>
From:   Yosry Ahmed <yosryahmed@google.com>
Date:   Mon, 3 Apr 2023 13:39:29 -0700
Message-ID: <CAJD7tkZF+rCNW4pctjOfAetoAQRq7-exV-j-nRc_xYMkMBGY_A@mail.gmail.com>
Subject: Re: [PATCH v2 4/9] cgroup: rstat: add WARN_ON_ONCE() if flushing
 outside task context
To:     Michal Hocko <mhocko@suse.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Shakeel Butt <shakeelb@google.com>, Tejun Heo <tj@kernel.org>,
        Josef Bacik <josef@toxicpanda.com>,
        Jens Axboe <axboe@kernel.dk>,
        Zefan Li <lizefan.x@bytedance.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Muchun Song <muchun.song@linux.dev>,
        Andrew Morton <akpm@linux-foundation.org>,
        =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>,
        Vasily Averin <vasily.averin@linux.dev>,
        cgroups@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        bpf@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Mon, Apr 3, 2023 at 1:38=E2=80=AFAM Michal Hocko <mhocko@suse.com> wrote=
:
>
> On Fri 31-03-23 12:03:47, Yosry Ahmed wrote:
> > On Fri, Mar 31, 2023 at 4:02=E2=80=AFAM Michal Hocko <mhocko@suse.com> =
wrote:
> > >
> > > On Thu 30-03-23 01:53:38, Yosry Ahmed wrote:
> > > [...]
> > > > Maybe we can add a primitive like might_sleep() for this, just food=
 for thought.
> > >
> > > I do not think it is the correct to abuse might_sleep if the function
> > > itself doesn't sleep. If it does might_sleep is already involved.
> >
> > Oh, sorry if I wasn't clear, I did not mean to reuse might_sleep() --
> > I meant introducing a new similar debug primitive that shouts if irqs
> > are disabled.
>
> This is circling back to original concerns about arbitrary decision to
> care about IRQs. Is this really any different from spin locks or preempt
> disabled critical sections preventing any scheduling and potentially
> triggereing soft lockups?

Not really, I am sure there are other code paths that may cause
similar problems. At least we can start annotating them so that we
don't regress them (e.g. by introducing a caller that disables irqs --
converting them into hard lockups).

> --
> Michal Hocko
> SUSE Labs