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authorJiri Kosina <jkosina@suse.cz>2012-07-27 10:38:50 +0000
committerDavid S. Miller <davem@davemloft.net>2012-07-27 13:45:51 -0700
commit59ea33a68a9083ac98515e4861c00e71efdc49a1 (patch)
tree709ce54c4ab4e140d8fa77ed63b3711445d9ac79 /net
parent6081030769f23c83c0564e993be146db568bf68b (diff)
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 <jkosina@suse.cz> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/ipv4/tcp_input.c4
1 files changed, 3 insertions, 1 deletions
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;
}