[PATCH 5.4 5/8] sctp: not disable bh in the whole sctp_get_port_local()

[Greg Kroah-Hartman]

From: Xin Long <lucien....@gmail.com>

[ Upstream commit 3106ecb43a05dc3e009779764b9da245a5d082de ]

With disabling bh in the whole sctp_get_port_local(), when
snum == 0 and too many ports have been used, the do-while
loop will take the cpu for a long time and cause cpu stuck:

  [ ] watchdog: BUG: soft lockup - CPU#11 stuck for 22s!
  [ ] RIP: 0010:native_queued_spin_lock_slowpath+0x4de/0x940
  [ ] Call Trace:
  [ ]  _raw_spin_lock+0xc1/0xd0
  [ ]  sctp_get_port_local+0x527/0x650 [sctp]
  [ ]  sctp_do_bind+0x208/0x5e0 [sctp]
  [ ]  sctp_autobind+0x165/0x1e0 [sctp]
  [ ]  sctp_connect_new_asoc+0x355/0x480 [sctp]
  [ ]  __sctp_connect+0x360/0xb10 [sctp]

There's no need to disable bh in the whole function of
sctp_get_port_local. So fix this cpu stuck by removing
local_bh_disable() called at the beginning, and using
spin_lock_bh() instead.

The same thing was actually done for inet_csk_get_port() in
Commit ea8add2b1903 ("tcp/dccp: better use of ephemeral
ports in bind()").

Thanks to Marcelo for pointing the buggy code out.

v1->v2:
  - use cond_resched() to yield cpu to other tasks if needed,
    as Eric noticed.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Ying Xu <yi...@redhat.com>
Signed-off-by: Xin Long <lucien....@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leit...@gmail.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/sctp/socket.c |   16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -8176,8 +8176,6 @@ static int sctp_get_port_local(struct so
 
        pr_debug("%s: begins, snum:%d\n", __func__, snum);
 
-       local_bh_disable();
-
        if (snum == 0) {
                /* Search for an available port. */
                int low, high, remaining, index;
@@ -8196,20 +8194,21 @@ static int sctp_get_port_local(struct so
                                continue;
                        index = sctp_phashfn(sock_net(sk), rover);
                        head = &sctp_port_hashtable[index];
-                       spin_lock(&head->lock);
+                       spin_lock_bh(&head->lock);
                        sctp_for_each_hentry(pp, &head->chain)
                                if ((pp->port == rover) &&
                                    net_eq(sock_net(sk), pp->net))
                                        goto next;
                        break;
                next:
-                       spin_unlock(&head->lock);
+                       spin_unlock_bh(&head->lock);
+                       cond_resched();
                } while (--remaining > 0);
 
                /* Exhausted local port range during search? */
                ret = 1;
                if (remaining <= 0)
-                       goto fail;
+                       return ret;
 
                /* OK, here is the one we will use.  HEAD (the port
                 * hash table list entry) is non-NULL and we hold it's
@@ -8224,7 +8223,7 @@ static int sctp_get_port_local(struct so
                 * port iterator, pp being NULL.
                 */
                head = &sctp_port_hashtable[sctp_phashfn(sock_net(sk), snum)];
-               spin_lock(&head->lock);
+               spin_lock_bh(&head->lock);
                sctp_for_each_hentry(pp, &head->chain) {
                        if ((pp->port == snum) && net_eq(pp->net, sock_net(sk)))
                                goto pp_found;
@@ -8324,10 +8323,7 @@ success:
        ret = 0;
 
 fail_unlock:
-       spin_unlock(&head->lock);
-
-fail:
-       local_bh_enable();
+       spin_unlock_bh(&head->lock);
        return ret;
 }