On Thu, Jan 10, 2019 at 01:53:28PM +0100, Dmitry Vyukov wrote: > On Thu, Jan 10, 2019 at 1:41 PM Peter Zijlstra <pet...@infradead.org> wrote: > > > > On Tue, Jan 08, 2019 at 11:37:46PM +0100, Florian Westphal wrote: > > > Anatol Pomozov <anatol.pomo...@gmail.com> wrote: > > > > Or maybe xt_replace_table() can be enhanced? When I hear that > > > > something waits until an event happens on all CPUs I think about > > > > wait_event() function. Would it be better for xt_replace_table() to > > > > introduce an atomic counter that is decremented by CPUs, and the main > > > > CPU waits until the counter gets zero? > > > > > > That would mean placing an additional atomic op into the > > > iptables evaluation path (ipt_do_table and friends). > > > > > > > For: > > > > /* > > * Ensure contents of newinfo are visible before assigning to > > * private. > > */ > > smp_wmb(); > > table->private = newinfo; > > > > we have: > > > > smp_store_release(&table->private, newinfo); > > > > But what store does that second smp_wmb() order against? The comment: > > > > /* make sure all cpus see new ->private value */ > > smp_wmb(); > > > > makes no sense what so ever, no smp_*() barrier can provide such > > guarantees. > > Do we want WRITE_ONCE here then?
The smp_store_release() already implies WRITE_ONCE().
