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net: nps_enet: Tx handler synchronization

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Below is a description of a possible problematic
sequence. CPU-A is sending a frame and CPU-B handles
the interrupt that indicates the frame was sent. CPU-B
reads an invalid value of tx_packet_sent.

	CPU-A				CPU-B
	-----				-----
	nps_enet_send_frame
	.
	.
	tx_skb = skb
	tx_packet_sent = true
	order HW to start tx
	.
	.
	HW complete tx
			    ------> 	get tx complete interrupt
					.
					.
					if(tx_packet_sent == true)
						handle tx_skb

	end memory transaction
	(tx_packet_sent actually
	 written)

Furthermore there is a dependency between tx_skb and tx_packet_sent.
There is no assurance that tx_skb contains a valid pointer at CPU B
when it sees tx_packet_sent == true.

Solution:

Initialize tx_skb to NULL and use it to indicate that packet was sent,
in this way tx_packet_sent can be removed.
Add a write memory barrier after setting tx_skb in order to make sure
that it is valid before HW is informed and IRQ is fired.

Fixed sequence will be:

       CPU-A                           CPU-B
       -----                           -----

	tx_skb = skb
	wmb()
	.
	.
	order HW to start tx
	.
	.
	HW complete tx
			------>		get tx complete interrupt
					.
					.
					if(tx_skb != NULL)
						handle tx_skb

					tx_skb = NULL

Signed-off-by: Elad Kanfi <eladkan@mellanox.com>
Acked-by: Noam Camus <noamca@mellanox.com>
Acked-by: Gilad Ben-Yossef <giladby@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Elad Kanfi
2016-05-09 20:13:19 +03:00
committed by David S. Miller
parent d99079e2fb
commit e5df49d564
2 changed files with 9 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/net/ethernet/ezchip/nps_enet.h
View File

@@ -165,14 +165,12 @@
* struct nps_enet_priv - Storage of ENET's private information.
* @regs_base: Base address of ENET memory-mapped control registers.
* @irq: For RX/TX IRQ number.
* @tx_packet_sent: SW indication if frame is being sent.
* @tx_skb: socket buffer of sent frame.
* @napi: Structure for NAPI.
*/
struct nps_enet_priv {
void __iomem *regs_base;
s32 irq;
bool tx_packet_sent;
struct sk_buff *tx_skb;
struct napi_struct napi;
u32 ge_mac_cfg_2_value;