On Mo, 2015-06-08 at 11:19 -0400, Neil Horman wrote:

On Mon, Jun 08, 2015 at 04:59:18PM +0200, Hannes Frederic Sowa wrote:

quoted

On Mon, Jun 8, 2015, at 16:46, Hannes Frederic Sowa wrote:

quoted

Hi Marcelo,

a few hints on rcuification, sorry I reviewed the code so late:

On Fri, Jun 5, 2015, at 19:08, mleitner@redhat.com wrote:

quoted

From: Marcelo Ricardo Leitner <marcelo.leitner@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.leitner@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..9e53412c4ed829e8e4577
7a6d95406d490dbaa75
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..9954fb8c9a9455d5ad7a6
27e2d7f9a1fef861fc2
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 ;) ).

quoted

+       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.

What makes you say that? Multiple contexts can issue mod_timer calls 
on the
same timer safely no, because of the internal locking?

That's true for timer handling but not to protect net->sctp.addr_waitq
list (Marcelo just explained it to me off-list). Looking at the patch
only in patchworks lost quite a lot of context you were already
discussing. ;)

We are currently checking if the double iteration can be avoided by
splicing addr_waitq on the local stack while holding the spin_lock and
later on notifying the sockets.

Bye,
Hannes