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SubjectRe: [PATCH] drivers: net: xgene: fix: Out of order descriptor bytes read
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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@apm.com>
> Signed-off-by: Keyur Chudgar <kchudgar@apm.com>
> Tested-by: Mark Langsdorf <mlangsdo@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)))
> break;
>
> + /* read fpqnum field after dataaddr field */
> + smp_rmb();
> if (is_rx_desc(raw_desc))
> ret = xgene_enet_rx_frame(ring, raw_desc);
> else

Reading your changelog, it looks like you need a plain rmb() here.





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