[PATCH] drivers: net: xgene: fix: Out of order descriptor bytes read
isubramanian at apm.com
Mon Jan 26 13:12:23 PST 2015
On Thu, Jan 22, 2015 at 2:50 PM, Eric Dumazet <eric.dumazet at gmail.com> wrote:
> On Thu, 2015-01-22 at 12:03 -0800, Iyappan Subramanian wrote:
>> This patch fixes the following kernel crash,
>> WARNING: CPU: 2 PID: 0 at net/ipv4/tcp_input.c:3079 tcp_clean_rtx_queue+0x658/0x80c()
>> Call trace:
>> Software writes poison data into the descriptor bytes[15:8] and upon
>> receiving the interrupt, if those bytes are overwritten by the hardware with
>> the valid data, software also reads bytes[7:0] and executes receive/tx
>> completion logic.
>> If the CPU executes the above two reads in out of order fashion, then the
>> bytes[7:0] will have older data and causing the kernel panic. We have to
>> force the order of the reads and thus this patch introduces read memory
>> barrier between these reads.
>> Signed-off-by: Iyappan Subramanian <isubramanian at apm.com>
>> Signed-off-by: Keyur Chudgar <kchudgar at apm.com>
>> Tested-by: Mark Langsdorf <mlangsdo at redhat.com>
>> drivers/net/ethernet/apm/xgene/xgene_enet_main.c | 2 ++
>> 1 file changed, 2 insertions(+)
>> diff --git a/drivers/net/ethernet/apm/xgene/xgene_enet_main.c b/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
>> index 83a5028..3622cdb 100644
>> --- a/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
>> +++ b/drivers/net/ethernet/apm/xgene/xgene_enet_main.c
>> @@ -369,6 +369,8 @@ static int xgene_enet_process_ring(struct xgene_enet_desc_ring *ring,
>> if (unlikely(xgene_enet_is_desc_slot_empty(raw_desc)))
>> + /* read fpqnum field after dataaddr field */
>> + smp_rmb();
>> if (is_rx_desc(raw_desc))
>> ret = xgene_enet_rx_frame(ring, raw_desc);
> Reading your changelog, it looks like you need a plain rmb() here.
rmb() translates into dsb, which in arm64 serializes everything
including instructions and thus expensive compared to dmb.
Do you see any issue with smp_rmb() (which translates into dmb) ?
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