On Tue, Oct 2, 2018 at 3:16 PM, Eric Dumazet <eduma...@google.com> wrote: > On Tue, Oct 2, 2018 at 1:19 AM Dmitry Vyukov <dvyu...@google.com> wrote: >> >> On Tue, Oct 2, 2018 at 7:49 AM, Eric Dumazet <eduma...@google.com> wrote: >> >> >> Does inet_frag_kill() hold fq->lock? I am missing how inet_frag_kill() >> and inet_frags_exit_net() are synchronized. >> Since you use smp_store_release()/READ_ONCE() they seem to run in >> parallel. But then isn't it possible that inet_frag_kill() reads >> nf->dead == 0, then inet_frags_exit_net() sets nf->dead, and then we >> have the same race on concurrent removal? Or, isn't it possible that >> inet_frag_kill() reads nf->dead == 1, but does not set >> INET_FRAG_HASH_DEAD yet, and then inet_frags_free_cb() misses the >> INET_FRAG_HASH_DEAD flag? >> > > Yes this is kind of implied in my patch. > I put the smp_store_release() and READ_ONCE exactly to document the > possible races. > This was the reason for my attempt in V1, doing a walk, but Herbert > said walk was not designed for doing deletes. > > Proper synch will need a synchronize_rcu(), and thus a future > conversion in net-next because we can not really > add new synchronize_rcu() calls in an (struct > pernet_operations.)exit() without considerable performance hit of > netns dismantles. > > So this will require a conversion of all inet_frags_exit_net() callers > to .exit_batch() to mitigate the cost. > > I thought of synchronize_rcu_bh() but this beast is going away soon anyway.
But if this patch allows all the same races and corruptions, then what's the point?
