tipc: remove subscription references only for pending timers

In commit, 139bb36f ("tipc: advance the time of deleting
subscription from subscriber->subscrp_list"), we delete the
subscription from the subscribers list and from nametable
unconditionally. This leads to the following bug if the timer
running tipc_subscrp_timeout() in another CPU accesses the
subscription list after the subscription delete request.

[39.570] general protection fault: 0000 [#1] SMP
::
[39.574] task: ffffffff81c10540 task.stack: ffffffff81c00000
[39.575] RIP: 0010:tipc_subscrp_timeout+0x32/0x80 [tipc]
[39.576] RSP: 0018:ffff88003ba03e90 EFLAGS: 00010282
[39.576] RAX: dead000000000200 RBX: ffff88003f0f3600 RCX: 0000000000000101
[39.577] RDX: dead000000000100 RSI: 0000000000000201 RDI: ffff88003f0d7948
[39.578] RBP: ffff88003ba03ea0 R08: 0000000000000001 R09: ffff88003ba03ef8
[39.579] R10: 000000000000014f R11: 0000000000000000 R12: ffff88003f0d7948
[39.580] R13: ffff88003f0f3618 R14: ffffffffa006c250 R15: ffff88003f0f3600
[39.581] FS:  0000000000000000(0000) GS:ffff88003ba00000(0000) knlGS:0000000000000000
[39.582] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[39.583] CR2: 00007f831c6e0714 CR3: 000000003d3b0000 CR4: 00000000000006f0
[39.584] Call Trace:
[39.584]  <IRQ>
[39.585]  call_timer_fn+0x3d/0x180
[39.585]  ? tipc_subscrb_rcv_cb+0x260/0x260 [tipc]
[39.586]  run_timer_softirq+0x168/0x1f0
[39.586]  ? sched_clock_cpu+0x16/0xc0
[39.587]  __do_softirq+0x9b/0x2de
[39.587]  irq_exit+0x60/0x70
[39.588]  smp_apic_timer_interrupt+0x3d/0x50
[39.588]  apic_timer_interrupt+0x86/0x90
[39.589] RIP: 0010:default_idle+0x20/0xf0
[39.589] RSP: 0018:ffffffff81c03e58 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff10
[39.590] RAX: 0000000000000000 RBX: ffffffff81c10540 RCX: 0000000000000000
[39.591] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
[39.592] RBP: ffffffff81c03e68 R08: 0000000000000000 R09: 0000000000000000
[39.593] R10: ffffc90001cbbe00 R11: 0000000000000000 R12: 0000000000000000
[39.594] R13: ffffffff81c10540 R14: 0000000000000000 R15: 0000000000000000
[39.595]  </IRQ>
::
[39.603] RIP: tipc_subscrp_timeout+0x32/0x80 [tipc] RSP: ffff88003ba03e90
[39.604] ---[ end trace 79ce94b7216cb459 ]---

Fixes: 139bb36f ("tipc: advance the time of deleting subscription from subscriber->subscrp_list")
Signed-off-by: NParthasarathy Bhuvaragan <parthasarathy.bhuvaragan@ericsson.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/tipc/subscr.c

@@ -52,7 +52,6 @@ struct tipc_subscriber {
 	struct list_head subscrp_list;
 };
 
-static void tipc_subscrp_delete(struct tipc_subscription *sub);
 static void tipc_subscrb_put(struct tipc_subscriber *subscriber);
 
 /**
@@ -197,15 +196,19 @@ static void tipc_subscrb_subscrp_delete(struct tipc_subscriber *subscriber,
 {
 	struct list_head *subscription_list = &subscriber->subscrp_list;
 	struct tipc_subscription *sub, *temp;
+	u32 timeout;
 
 	spin_lock_bh(&subscriber->lock);
 	list_for_each_entry_safe(sub, temp, subscription_list,  subscrp_list) {
 		if (s && memcmp(s, &sub->evt.s, sizeof(struct tipc_subscr)))
 			continue;
 
-		tipc_nametbl_unsubscribe(sub);
-		list_del(&sub->subscrp_list);
-		tipc_subscrp_delete(sub);
+		timeout = htohl(sub->evt.s.timeout, sub->swap);
+		if (timeout == TIPC_WAIT_FOREVER || del_timer(&sub->timer)) {
+			tipc_nametbl_unsubscribe(sub);
+			list_del(&sub->subscrp_list);
+			tipc_subscrp_put(sub);
+		}
 
 		if (s)
 			break;
@@ -236,14 +239,6 @@ static void tipc_subscrb_delete(struct tipc_subscriber *subscriber)
 	tipc_subscrb_put(subscriber);
 }
 
-static void tipc_subscrp_delete(struct tipc_subscription *sub)
-{
-	u32 timeout = htohl(sub->evt.s.timeout, sub->swap);
-
-	if (timeout == TIPC_WAIT_FOREVER || del_timer(&sub->timer))
-		tipc_subscrp_put(sub);
-}
-
 static void tipc_subscrp_cancel(struct tipc_subscr *s,
 				struct tipc_subscriber *subscriber)
 {