[PATCH 2/2] pptp: Reset call_id as 0 to avoid one useless lookup at next time

[fgao]

From: Gao Feng <f...@ikuai8.com>

When pptp fails to get valid callid, the global call_id is set as
MAX_CALLID. Then it must fail to get callid at next time, when
invoke find_next_zero_bit from call_id+1. Because the call_id+1
exceeds the limit "MAX_CALLID".
So reset call_id as 0 when fail to get valid callid. And add one
variable to check if need the second lookup.

Signed-off-by: Gao Feng <f...@ikuai8.com>
---
 v1: Initial patch

 drivers/net/ppp/pptp.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ppp/pptp.c b/drivers/net/ppp/pptp.c
index 48c3701..9afef3c 100644
--- a/drivers/net/ppp/pptp.c
+++ b/drivers/net/ppp/pptp.c
@@ -103,12 +103,21 @@ static int add_chan(struct pppox_sock *sock,
        static int call_id;
 
        spin_lock(&chan_lock);
-       if (!sa->call_id)       {
+       if (!sa->call_id) {
+               bool from_start = (call_id == 0);
+
                call_id = find_next_zero_bit(callid_bitmap, MAX_CALLID, call_id 
+ 1);
                if (call_id == MAX_CALLID) {
-                       call_id = find_next_zero_bit(callid_bitmap, MAX_CALLID, 
1);
-                       if (call_id == MAX_CALLID)
+                       if (unlikely(from_start)) {
+                               call_id = 0;
                                goto out_err;
+                       } else {
+                               call_id = find_next_zero_bit(callid_bitmap, 
MAX_CALLID, 1);
+                               if (call_id == MAX_CALLID) {
+                                       call_id = 0;
+                                       goto out_err;
+                               }
+                       }
                }
                sa->call_id = call_id;
        } else if (test_bit(sa->call_id, callid_bitmap)) {
@@ -656,8 +665,10 @@ static int __init pptp_init_module(void)
        pr_info("PPTP driver version " PPTP_DRIVER_VERSION "\n");
 
        callid_sock = vzalloc((MAX_CALLID + 1) * sizeof(void *));
-       if (!callid_sock)
+       if (!callid_sock) {
+               pr_err("PPTP: can't alloc callid_sock mem");
                return -ENOMEM;
+       }
 
        err = gre_add_protocol(&gre_pptp_protocol, GREPROTO_PPTP);
        if (err) {
-- 
1.9.1