On Wed, Oct 31, 2018 at 4:10 PM Igor Stoppa <igor.stoppa@xxxxxxxxx> wrote: > > > > On 01/11/2018 00:57, Andy Lutomirski wrote: > > > > > >> On Oct 31, 2018, at 2:00 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > >> I _think_ the use-case for atomics is updating the reference counts of > >> objects that are in this write-rare domain. But I'm not entirely clear > >> on that myself either. I just really want to avoid duplicating that > >> stuff. > > > > Sounds nuts. Doing a rare-write is many hundreds of cycles at best. Using that for a reference count sounds wacky. > > > > Can we see a *real* use case before we over complicate the API? > > > > > Does patch #14 of this set not qualify? ima_htable.len ? > > https://www.openwall.com/lists/kernel-hardening/2018/10/23/20 > Do you mean this (sorry for whitespace damage): + pratomic_long_inc(&ima_htable.len); - atomic_long_inc(&ima_htable.len); if (update_htable) { key = ima_hash_key(entry->digest); - hlist_add_head_rcu(&qe->hnext, &ima_htable.queue[key]); + prhlist_add_head_rcu(&qe->hnext, &ima_htable.queue[key]); } ISTM you don't need that atomic operation -- you could take a spinlock and then just add one directly to the variable. --Andy
