On 2015-01-12 12:44:56 -0500, Robert Haas wrote: > On Mon, Jan 12, 2015 at 11:27 AM, Andres Freund <and...@2ndquadrant.com> > wrote: > > On 2015-01-12 11:03:42 -0500, Tom Lane wrote: > >> Andres Freund <and...@2ndquadrant.com> writes: > >> > While it might not be required for existing latch uses (I'm *not* sure > >> > that's true) > > > > I think at least syncrep.c might not be correct. In SyncRepWakeQueue() > > it sets PGPROC->syncRepState without the necessary barriers (via locks), > > although it does use them in SyncRepWaitForLSN(). > > > > It is, perhaps surprisingly to many, not sufficient to take a spinlock, > > change the flag, release it and then set the latch - the release alone > > doesn't guarantee a sufficient barrier unless looking at the flag is > > also protected by the spinlock. > > I thought we decided that a spinlock acquire or release should be a > full barrier.
Acquire + release, yes. But not release alone? The x86 spinlock release currently is just a store - that won't ever be a full barrier. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
