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Message-ID: <20250220163226.42wlaewgfueeezj3@skbuf>
Date: Thu, 20 Feb 2025 18:32:26 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: Wei Fang <wei.fang@....com>
Cc: claudiu.manoil@....com, xiaoning.wang@....com, andrew+netdev@...n.ch,
davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
pabeni@...hat.com, ioana.ciornei@....com, yangbo.lu@....com,
michal.swiatkowski@...ux.intel.com, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, imx@...ts.linux.dev,
stable@...r.kernel.org
Subject: Re: [PATCH v2 net 9/9] net: enetc: fix the off-by-one issue in
enetc_map_tx_tso_buffs()
On Wed, Feb 19, 2025 at 01:42:47PM +0800, Wei Fang wrote:
> There is an off-by-one issue for the err_chained_bd path, it will free
> one more tx_swbd than expected. But there is no such issue for the
> err_map_data path.
It's clear that one of err_chained_bd or err_map_data is wrong, because
they operate with a different "count" but same "i". But how did you
determine which one is wrong? Is it based on static analysis? Because I
think the other one is wrong, more below.
> To fix this off-by-one issue and make the two error
> handling consistent, the loop condition of error handling is modified
> and the 'count++' operation is moved before enetc_map_tx_tso_data().
>
> Fixes: fb8629e2cbfc ("net: enetc: add support for software TSO")
> Cc: stable@...r.kernel.org
> Signed-off-by: Wei Fang <wei.fang@....com>
> ---
> drivers/net/ethernet/freescale/enetc/enetc.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
> index 9a24d1176479..fe3967268a19 100644
> --- a/drivers/net/ethernet/freescale/enetc/enetc.c
> +++ b/drivers/net/ethernet/freescale/enetc/enetc.c
> @@ -832,6 +832,7 @@ static int enetc_map_tx_tso_buffs(struct enetc_bdr *tx_ring, struct sk_buff *skb
> txbd = ENETC_TXBD(*tx_ring, i);
> tx_swbd = &tx_ring->tx_swbd[i];
> prefetchw(txbd);
> + count++;
>
> /* Compute the checksum over this segment of data and
> * add it to the csum already computed (over the L4
> @@ -848,7 +849,6 @@ static int enetc_map_tx_tso_buffs(struct enetc_bdr *tx_ring, struct sk_buff *skb
> goto err_map_data;
>
> data_len -= size;
> - count++;
> bd_data_num++;
> tso_build_data(skb, &tso, size);
>
> @@ -874,13 +874,13 @@ static int enetc_map_tx_tso_buffs(struct enetc_bdr *tx_ring, struct sk_buff *skb
> dev_err(tx_ring->dev, "DMA map error");
>
> err_chained_bd:
> - do {
> + while (count--) {
> tx_swbd = &tx_ring->tx_swbd[i];
> enetc_free_tx_frame(tx_ring, tx_swbd);
> if (i == 0)
> i = tx_ring->bd_count;
> i--;
> - } while (count--);
> + }
>
> return 0;
> }
ah, there you go, here's the 3rd instance of TX DMA buffer unmapping :-/
Forget what I said in reply to patch 1/9 about having common code later.
After going through the whole set and now seeing this, I now think it's
better that you create the helper now, and consolidate the 2 instances
you touch anyway. Later you can make enetc_lso_hw_offload() reuse this
helper in net-next.
It should be something like this in the end (sorry, just 1 squashed diff):
diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
index 6178157611db..a70e92dcbe2c 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c
@@ -106,6 +106,24 @@ static void enetc_free_tx_frame(struct enetc_bdr *tx_ring,
}
}
+/**
+ * enetc_unwind_tx_frame() - Unwind the DMA mappings of a multi-buffer TX frame
+ * @tx_ring: Pointer to the TX ring on which the buffer descriptors are located
+ * @count: Number of TX buffer descriptors which need to be unmapped
+ * @i: Index of the last successfully mapped TX buffer descriptor
+ */
+static void enetc_unwind_tx_frame(struct enetc_bdr *tx_ring, int count, int i)
+{
+ while (count--) {
+ struct enetc_tx_swbd *tx_swbd = &tx_ring->tx_swbd[i];
+
+ enetc_free_tx_frame(tx_ring, tx_swbd);
+ if (i == 0)
+ i = tx_ring->bd_count;
+ i--;
+ }
+}
+
/* Let H/W know BD ring has been updated */
static void enetc_update_tx_ring_tail(struct enetc_bdr *tx_ring)
{
@@ -399,13 +417,7 @@ static int enetc_map_tx_buffs(struct enetc_bdr *tx_ring, struct sk_buff *skb)
dma_err:
dev_err(tx_ring->dev, "DMA map error");
- while (count--) {
- tx_swbd = &tx_ring->tx_swbd[i];
- enetc_free_tx_frame(tx_ring, tx_swbd);
- if (i == 0)
- i = tx_ring->bd_count;
- i--;
- }
+ enetc_unwind_tx_frame(tx_ring, count, i);
return 0;
}
@@ -752,7 +764,6 @@ static int enetc_lso_map_data(struct enetc_bdr *tx_ring, struct sk_buff *skb,
static int enetc_lso_hw_offload(struct enetc_bdr *tx_ring, struct sk_buff *skb)
{
- struct enetc_tx_swbd *tx_swbd;
struct enetc_lso_t lso = {0};
int err, i, count = 0;
@@ -776,13 +787,7 @@ static int enetc_lso_hw_offload(struct enetc_bdr *tx_ring, struct sk_buff *skb)
return count;
dma_err:
- do {
- tx_swbd = &tx_ring->tx_swbd[i];
- enetc_free_tx_frame(tx_ring, tx_swbd);
- if (i == 0)
- i = tx_ring->bd_count;
- i--;
- } while (--count);
+ enetc_unwind_tx_frame(tx_ring, count, i);
return 0;
}
@@ -877,13 +882,7 @@ static int enetc_map_tx_tso_buffs(struct enetc_bdr *tx_ring, struct sk_buff *skb
dev_err(tx_ring->dev, "DMA map error");
err_chained_bd:
- while (count--) {
- tx_swbd = &tx_ring->tx_swbd[i];
- enetc_free_tx_frame(tx_ring, tx_swbd);
- if (i == 0)
- i = tx_ring->bd_count;
- i--;
- }
+ enetc_unwind_tx_frame(tx_ring, count, i);
return 0;
}
With the definitions laid out explicitly in a kernel-doc, doesn't the
rest of the patch look a bit wrong? Why would you increment "count"
before enetc_map_tx_tso_data() succeeds? Why isn't the problem that "i"
needs to be rolled back on enetc_map_tx_tso_data() failure instead?
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