linux-kernel - Re: [tip: timers/core] hrtimer: Annotate lockless access to timer->state

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Message-ID: <CANn89iL=xPxejRPC=wHY7q27fLOvFBK-7HtqU_HJo+go3S9UXA@mail.gmail.com>
Date:   Wed, 6 Nov 2019 14:59:36 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     LKML <linux-kernel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>
Cc:     linux-tip-commits@...r.kernel.org,
        syzbot <syzkaller@...glegroups.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>
Subject: Re: [tip: timers/core] hrtimer: Annotate lockless access to timer->state

On Wed, Nov 6, 2019 at 2:53 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Wed, Nov 6, 2019 at 2:24 PM tip-bot2 for Eric Dumazet
> <tip-bot2@...utronix.de> wrote:
> >
> > The following commit has been merged into the timers/core branch of tip:
> >
> > Commit-ID:     56144737e67329c9aaed15f942d46a6302e2e3d8
> > Gitweb:        https://git.kernel.org/tip/56144737e67329c9aaed15f942d46a6302e2e3d8
> > Author:        Eric Dumazet <edumazet@...gle.com>
> > AuthorDate:    Wed, 06 Nov 2019 09:48:04 -08:00
> > Committer:     Thomas Gleixner <tglx@...utronix.de>
> > CommitterDate: Wed, 06 Nov 2019 23:18:31 +01:00
> >
> > hrtimer: Annotate lockless access to timer->state
> >
>
> I guess we also need to fix timer_pending(), since timer->entry.pprev
> could change while we read it.
>

It is interesting seeing hlist_add_head() has a WRITE_ONCE(h->first, n);,
but no WRITE_ONCE() for the pprev change.

The WRITE_ONCE() was added in commit 1c97be677f72b3c338312aecd36d8fff20322f32
("list: Use WRITE_ONCE() when adding to lists and hlists")