Messages in this thread | | | Date | Thu, 7 Nov 2019 00:52:55 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [tip: timers/core] hrtimer: Annotate lockless access to timer->state |
| |
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
| |