From: Jiri Kosina Date: Fri, 27 Jul 2012 10:38:50 +0000 (+0000) Subject: tcp: perform DMA to userspace only if there is a task waiting for it X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=59ea33a68a9083ac98515e4861c00e71efdc49a1;p=deliverable%2Flinux.git tcp: perform DMA to userspace only if there is a task waiting for it Back in 2006, commit 1a2449a87b ("[I/OAT]: TCP recv offload to I/OAT") added support for receive offloading to IOAT dma engine if available. The code in tcp_rcv_established() tries to perform early DMA copy if applicable. It however does so without checking whether the userspace task is actually expecting the data in the buffer. This is not a problem under normal circumstances, but there is a corner case where this doesn't work -- and that's when MSG_TRUNC flag to recvmsg() is used. If the IOAT dma engine is not used, the code properly checks whether there is a valid ucopy.task and the socket is owned by userspace, but misses the check in the dmaengine case. This problem can be observed in real trivially -- for example 'tbench' is a good reproducer, as it makes a heavy use of MSG_TRUNC. On systems utilizing IOAT, you will soon find tbench waiting indefinitely in sk_wait_data(), as they have been already early-copied in tcp_rcv_established() using dma engine. This patch introduces the same check we are performing in the simple iovec copy case to the IOAT case as well. It fixes the indefinite recvmsg(MSG_TRUNC) hangs. Signed-off-by: Jiri Kosina Signed-off-by: David S. Miller --- diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index aa659e825054..a356e1fecf9a 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -5475,7 +5475,9 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb, if (tp->copied_seq == tp->rcv_nxt && len - tcp_header_len <= tp->ucopy.len) { #ifdef CONFIG_NET_DMA - if (tcp_dma_try_early_copy(sk, skb, tcp_header_len)) { + if (tp->ucopy.task == current && + sock_owned_by_user(sk) && + tcp_dma_try_early_copy(sk, skb, tcp_header_len)) { copied_early = 1; eaten = 1; }