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-Tag: v3.2.28~27 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=789e0ed6c1132db40b4e6349113516ea0f700710;p=pandora-kernel.git tcp: perform DMA to userspace only if there is a task waiting for it [ Upstream commit 59ea33a68a9083ac98515e4861c00e71efdc49a1 ] 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 Signed-off-by: Ben Hutchings --- Reading git-diff-tree failed