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

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Message-ID: <CAHk-=wiZ=oic3UfejGzy_31RYggtZWUeF1gE82_NHAA=ENY6Kw@mail.gmail.com>
Date:   Mon, 10 Jan 2022 09:42:13 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
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 9:25 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?

                   Linus