linux-kernel - Re: psi_trigger_poll() is completely broken

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Message-ID: <CAJuCfpFFQx525=d8odiiAyi6w5M6KKx-1726zvuV=eADPB8wKg@mail.gmail.com>
Date:   Mon, 10 Jan 2022 10:19:01 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Eric Biggers <ebiggers@...nel.org>, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Hillf Danton <hdanton@...a.com>,
        syzbot <syzbot+cdb5dd11c97cc532efad@...kaller.appspotmail.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: psi_trigger_poll() is completely broken

On Mon, Jan 10, 2022 at 9:42 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Mon, Jan 10, 2022 at 9:25 AM Suren Baghdasaryan <surenb@...gle.com> wrote:
> >
> > About the issue of serializing concurrent writes for
> > cgroup_pressure_write() similar to how psi_write() does. Doesn't
> > of->mutex inside kernfs_fop_write_iter() serialize the writes to the
> > same file?
>
> Ahh, yes, it looks like that does solve the serialization issue.
> Sorry, I missed that because I'm not actually all that familiar with
> the kernfs 'of' code.
>
> So the only issue is the trigger lifetime one, and if a single trigger
> is sufficient and returning -EBUSY for trying to replace an existing
> one is good, then I think that's the proper fix.
>
> I'm very busy with the merge window (and some upcoming travel and
> family events), so I'm hoping somebody will write and test such a
> patch. Please?

Yes, definitely. I'm on it. Will try posting it later today or
tomorrow morning if testing reveals something unexpected.
Thanks!

>
>                    Linus