This is a note to let you know that I've just added the patch titled net: renesas: sh_eth: Fix freeing wrong tx descriptor to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-renesas-sh_eth-fix-freeing-wrong-tx-descriptor.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 5ef945011746359c846a9d6285cc0e8b7c03740f Author: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx> Date: Tue Sep 7 20:29:40 2021 +0900 net: renesas: sh_eth: Fix freeing wrong tx descriptor [ Upstream commit 0341d5e3d1ee2a36dd5a49b5bef2ce4ad1cfa6b4 ] The cur_tx counter must be incremented after TACT bit of txdesc->status was set. However, a CPU is possible to reorder instructions and/or memory accesses between cur_tx and txdesc->status. And then, if TX interrupt happened at such a timing, the sh_eth_tx_free() may free the descriptor wrongly. So, add wmb() before cur_tx++. Otherwise NETDEV WATCHDOG timeout is possible to happen. Fixes: 86a74ff21a7a ("net: sh_eth: add support for Renesas SuperH Ethernet") Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/net/ethernet/renesas/sh_eth.c b/drivers/net/ethernet/renesas/sh_eth.c index 1942264b621b..73fc8e9683b7 100644 --- a/drivers/net/ethernet/renesas/sh_eth.c +++ b/drivers/net/ethernet/renesas/sh_eth.c @@ -2426,6 +2426,7 @@ static int sh_eth_start_xmit(struct sk_buff *skb, struct net_device *ndev) else txdesc->status |= cpu_to_edmac(mdp, TD_TACT); + wmb(); /* cur_tx must be incremented after TACT bit was set */ mdp->cur_tx++; if (!(sh_eth_read(ndev, EDTRR) & sh_eth_get_edtrr_trns(mdp)))