Patch "net: renesas: rswitch: fix race window between tx start and complete" has been added to the 6.12-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    net: renesas: rswitch: fix race window between tx start and complete

to the 6.12-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-rswitch-fix-race-window-between-tx-start.patch
and it can be found in the queue-6.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit b82d0b0657f544dc16255b1743fad56014bf1979
Author: Nikita Yushchenko <nikita.yoush@xxxxxxxxxxxxxxxxxx>
Date:   Sun Dec 8 14:50:02 2024 +0500

    net: renesas: rswitch: fix race window between tx start and complete
    
    [ Upstream commit 0c9547e6ccf40455b0574cf589be3b152a3edf5b ]
    
    If hardware is already transmitting, it can start handling the
    descriptor being written to immediately after it observes updated DT
    field, before the queue is kicked by a write to GWTRC.
    
    If the start_xmit() execution is preempted at unfortunate moment, this
    transmission can complete, and interrupt handled, before gq->cur gets
    updated. With the current implementation of completion, this will cause
    the last entry not completed.
    
    Fix that by changing completion loop to check DT values directly, instead
    of depending on gq->cur.
    
    Fixes: 3590918b5d07 ("net: ethernet: renesas: Add support for "Ethernet Switch"")
    Signed-off-by: Nikita Yushchenko <nikita.yoush@xxxxxxxxxxxxxxxxxx>
    Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
    Link: https://patch.msgid.link/20241208095004.69468-3-nikita.yoush@xxxxxxxxxxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/net/ethernet/renesas/rswitch.c b/drivers/net/ethernet/renesas/rswitch.c
index 32b32aa7e01f..c251becef6f8 100644
--- a/drivers/net/ethernet/renesas/rswitch.c
+++ b/drivers/net/ethernet/renesas/rswitch.c
@@ -862,13 +862,10 @@ static void rswitch_tx_free(struct net_device *ndev)
 	struct rswitch_ext_desc *desc;
 	struct sk_buff *skb;
 
-	for (; rswitch_get_num_cur_queues(gq) > 0;
-	     gq->dirty = rswitch_next_queue_index(gq, false, 1)) {
-		desc = &gq->tx_ring[gq->dirty];
-		if ((desc->desc.die_dt & DT_MASK) != DT_FEMPTY)
-			break;
-
+	desc = &gq->tx_ring[gq->dirty];
+	while ((desc->desc.die_dt & DT_MASK) == DT_FEMPTY) {
 		dma_rmb();
+
 		skb = gq->skbs[gq->dirty];
 		if (skb) {
 			rdev->ndev->stats.tx_packets++;
@@ -879,7 +876,10 @@ static void rswitch_tx_free(struct net_device *ndev)
 			dev_kfree_skb_any(gq->skbs[gq->dirty]);
 			gq->skbs[gq->dirty] = NULL;
 		}
+
 		desc->desc.die_dt = DT_EEMPTY;
+		gq->dirty = rswitch_next_queue_index(gq, false, 1);
+		desc = &gq->tx_ring[gq->dirty];
 	}
 }
 
@@ -1685,6 +1685,8 @@ static netdev_tx_t rswitch_start_xmit(struct sk_buff *skb, struct net_device *nd
 	gq->skbs[(gq->cur + nr_desc - 1) % gq->ring_size] = skb;
 	gq->unmap_addrs[(gq->cur + nr_desc - 1) % gq->ring_size] = dma_addr_orig;
 
+	dma_wmb();
+
 	/* DT_FSTART should be set at last. So, this is reverse order. */
 	for (i = nr_desc; i-- > 0; ) {
 		desc = &gq->tx_ring[rswitch_next_queue_index(gq, true, i)];
@@ -1695,8 +1697,6 @@ static netdev_tx_t rswitch_start_xmit(struct sk_buff *skb, struct net_device *nd
 			goto err_unmap;
 	}
 
-	wmb();	/* gq->cur must be incremented after die_dt was set */
-
 	gq->cur = rswitch_next_queue_index(gq, true, nr_desc);
 	rswitch_modify(rdev->addr, GWTRC(gq->index), 0, BIT(gq->index % 32));