From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Ben Hutchings Subject: [ 30/72] sfc: Only use TX push if a single descriptor is to be written Date: Tue, 26 Mar 2013 15:51:13 -0700 Message-Id: <20130326224922.798146576@linuxfoundation.org> In-Reply-To: <20130326224919.675227837@linuxfoundation.org> References: <20130326224919.675227837@linuxfoundation.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ben Hutchings [ Upstream commit fae8563b25f73dc584a07bcda7a82750ff4f7672 ] Using TX push when notifying the NIC of multiple new descriptors in the ring will very occasionally cause the TX DMA engine to re-use an old descriptor. This can result in a duplicated or partly duplicated packet (new headers with old data), or an IOMMU page fault. This does not happen when the pushed descriptor is the only one written. TX push also provides little latency benefit when a packet requires more than one descriptor. Signed-off-by: Ben Hutchings Signed-off-by: Greg Kroah-Hartman --- drivers/net/ethernet/sfc/nic.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/drivers/net/ethernet/sfc/nic.c +++ b/drivers/net/ethernet/sfc/nic.c @@ -379,7 +379,8 @@ efx_may_push_tx_desc(struct efx_tx_queue return false; tx_queue->empty_read_count = 0; - return ((empty_read_count ^ write_count) & ~EFX_EMPTY_COUNT_VALID) == 0; + return ((empty_read_count ^ write_count) & ~EFX_EMPTY_COUNT_VALID) == 0 + && tx_queue->write_count - write_count == 1; } /* For each entry inserted into the software descriptor ring, create a