| Message ID | alpine.LNX.2.00.1207272237470.30412@pobox.suse.cz |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Jiri Kosina <jkosina@suse.cz> Date: Fri, 27 Jul 2012 22:38:50 +0200 (CEST) > 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 <jkosina@suse.cz> Applied. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 3e07a64..76e3bf6 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; }
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 <jkosina@suse.cz> --- net/ipv4/tcp_input.c | 4 +++- 1 files changed, 3 insertions(+), 1 deletions(-)