On Mon, Jun 8, 2015, at 16:46, Hannes Frederic Sowa wrote:
> Hi Marcelo,
>
> a few hints on rcuification, sorry I reviewed the code so late:
>
> On Fri, Jun 5, 2015, at 19:08, mleit...@redhat.com wrote:
> > From: Marcelo Ricardo Leitner <marcelo.leit...@gmail.com>
> >
> > That's needed for the next patch, so we break the lock inversion between
> > netns_sctp->addr_wq_lock and socket lock on
> > sctp_addr_wq_timeout_handler(). With this, we can traverse addr_waitq
> > without taking addr_wq_lock, taking it just for the write operations.
> >
> > Signed-off-by: Marcelo Ricardo Leitner <marcelo.leit...@gmail.com>
> > ---
> >
> > Notes:
> > v2->v3:
> > placed break statement on sctp_free_addr_wq_entry()
> > removed unnecessary spin_lock noticed by Neil
> >
> > include/net/netns/sctp.h | 2 +-
> > net/sctp/protocol.c | 80
> > +++++++++++++++++++++++++++++-------------------
> > 2 files changed, 49 insertions(+), 33 deletions(-)
> >
> > diff --git a/include/net/netns/sctp.h b/include/net/netns/sctp.h
> > index
> > 3573a81815ad9e0efb6ceb721eb066d3726419f0..9e53412c4ed829e8e45777a6d95406d490dbaa75
> > 100644
> > --- a/include/net/netns/sctp.h
> > +++ b/include/net/netns/sctp.h
> > @@ -28,7 +28,7 @@ struct netns_sctp {
> > * It is a list of sctp_sockaddr_entry.
> > */
> > struct list_head local_addr_list;
> > - struct list_head addr_waitq;
> > + struct list_head __rcu addr_waitq;
> > struct timer_list addr_wq_timer;
> > struct list_head auto_asconf_splist;
> > spinlock_t addr_wq_lock;
> > diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
> > index
> > 53b7acde9aa37bf3d4029c459421564d5270f4c0..9954fb8c9a9455d5ad7a627e2d7f9a1fef861fc2
> > 100644
> > --- a/net/sctp/protocol.c
> > +++ b/net/sctp/protocol.c
> > @@ -593,15 +593,47 @@ static void sctp_v4_ecn_capable(struct sock *sk)
> > INET_ECN_xmit(sk);
> > }
> >
> > +static void sctp_free_addr_wq(struct net *net)
> > +{
> > + struct sctp_sockaddr_entry *addrw;
> > +
> > + spin_lock_bh(&net->sctp.addr_wq_lock);
>
> Instead of holding spin_lock_bh you need to hold rcu_read_lock_bh, so
> kfree_rcu does not call free function at once (in theory ;) ).
>
> > + del_timer(&net->sctp.addr_wq_timer);
> > + list_for_each_entry_rcu(addrw, &net->sctp.addr_waitq, list) {
> > + list_del_rcu(&addrw->list);
> > + kfree_rcu(addrw, rcu);
> > + }
> > + spin_unlock_bh(&net->sctp.addr_wq_lock);
> > +}
> > +
> > +/* As there is no refcnt on sctp_sockaddr_entry, we must check inside
> > + * the lock if it wasn't removed from addr_waitq already, otherwise we
> > + * could double-free it.
> > + */
> > +static void sctp_free_addr_wq_entry(struct net *net,
> > + struct sctp_sockaddr_entry *addrw)
> > +{
> > + struct sctp_sockaddr_entry *temp;
> > +
> > + spin_lock_bh(&net->sctp.addr_wq_lock);
>
> I don't think this spin_lock operation is needed. The del_timer
> functions do synchronize themselves.
>
Sorry, those above two locks are needed, they are not implied by other
locks.
Bye,
Hannes
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