From: "Paul E. McKenney" <paulmck@kernel.org>
To: Eric Dumazet <edumazet@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
linux-tip-commits@vger.kernel.org,
syzbot <syzkaller@googlegroups.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>
Subject: Re: [tip: timers/core] hrtimer: Annotate lockless access to timer->state
Date: Thu, 7 Nov 2019 00:52:55 -0800 [thread overview]
Message-ID: <20191107085255.GK20975@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <CANn89iL=xPxejRPC=wHY7q27fLOvFBK-7HtqU_HJo+go3S9UXA@mail.gmail.com>
On Wed, Nov 06, 2019 at 02:59:36PM -0800, Eric Dumazet wrote:
> On Wed, Nov 6, 2019 at 2:53 PM Eric Dumazet <edumazet@google.com> wrote:
> >
> > On Wed, Nov 6, 2019 at 2:24 PM tip-bot2 for Eric Dumazet
> > <tip-bot2@linutronix.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@google.com>
> > > AuthorDate: Wed, 06 Nov 2019 09:48:04 -08:00
> > > Committer: Thomas Gleixner <tglx@linutronix.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")
The theory is that while the ->next pointer is concurrently accessed by
RCU readers, the ->pprev pointer is accessed only by updaters, who need
to supply sufficient synchronization.
But what is this theory missing in practice?
Thanx, Paul
next prev parent reply other threads:[~2019-11-07 8:53 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-06 17:48 [PATCH] hrtimer: Annotate lockless access to timer->state Eric Dumazet
2019-11-06 18:09 ` Thomas Gleixner
2019-11-06 18:19 ` Eric Dumazet
2019-11-06 19:15 ` Thomas Gleixner
2019-11-06 20:00 ` Eric Dumazet
2019-11-06 21:06 ` [tip: timers/core] " tip-bot2 for Eric Dumazet
2019-11-06 22:02 ` Eric Dumazet
2019-11-06 22:16 ` Thomas Gleixner
2019-11-06 22:24 ` tip-bot2 for Eric Dumazet
2019-11-06 22:53 ` Eric Dumazet
2019-11-06 22:59 ` Eric Dumazet
2019-11-07 8:52 ` Paul E. McKenney [this message]
2019-11-07 15:48 ` Eric Dumazet
2019-11-07 16:11 ` Paul E. McKenney
2019-11-07 16:35 ` Eric Dumazet
2019-11-07 16:39 ` Eric Dumazet
2019-11-07 16:54 ` Paul E. McKenney
2019-11-07 16:59 ` Eric Dumazet
2019-11-07 17:07 ` Paul E. McKenney
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