Commit 3fa6b5ad authored Apr 21, 2009 by Hendrik Brueckner Committed by David S. Miller Apr 21, 2009

af_iucv: Fix race when queuing incoming iucv messages



AF_IUCV runs into a race when queuing incoming iucv messages
and receiving the resulting backlog.

If the Linux system is under pressure (high load or steal time),
the message queue grows up, but messages are not received and queued
onto the backlog queue. In that case, applications do not
receive any data with recvmsg() even if AF_IUCV puts incoming
messages onto the message queue.

The race can be avoided if the message queue spinlock in the
message_pending callback is spreaded across the entire callback
function.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent e14ad5fa

net/iucv/af_iucv.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -1124,6 +1124,8 @@ static void iucv_callback_rx(struct iucv_path path, struct iucv_message msg)
		return;
		}

		spin_lock(&iucv->message_q.lock);

		if (!list_empty(&iucv->message_q.list) \|\|
		!skb_queue_empty(&iucv->backlog_skb_q))
		goto save_message;
		@@ -1137,9 +1139,8 @@ static void iucv_callback_rx(struct iucv_path path, struct iucv_message msg)
		if (!skb)
		goto save_message;

		spin_lock(&iucv->message_q.lock);
		iucv_process_message(sk, skb, path, msg);
		spin_unlock(&iucv->message_q.lock);
		goto out_unlock;

		return;

		@@ -1150,8 +1151,9 @@ save_message:
		save_msg->path = path;
		save_msg->msg = *msg;

		spin_lock(&iucv->message_q.lock);
		list_add_tail(&save_msg->list, &iucv->message_q.list);

		out_unlock:
		spin_unlock(&iucv->message_q.lock);
		}

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