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Tue, 31 Mar 2026 03:05:22 -0700 (PDT) Received: from [192.168.88.32] ([212.105.155.58]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4887adc52b2sm14522545e9.12.2026.03.31.03.05.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 31 Mar 2026 03:05:20 -0700 (PDT) Message-ID: <51dfd8ae-dc4e-4837-9b00-c596c457117e@redhat.com> Date: Tue, 31 Mar 2026 12:05:19 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] net: ns83820: check DMA mapping errors in hard_start_xmit To: Wang Jun <1742789905@qq.com>, kuba@kernel.org Cc: andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, simon.horman@corigine.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, gszhai@bjtu.edu.cn, 25125332@bjtu.edu.cn, 25125283@bjtu.edu.cn, 23120469@bjtu.edu.cn, stable@vger.kernel.org References: Content-Language: en-US From: Paolo Abeni In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/27/26 2:16 AM, Wang Jun wrote: > The ns83820 driver currently ignores the return values of dma_map_single() > and skb_frag_dma_map() in the transmit path. If DMA mapping fails due to > IOMMU exhaustion or SWIOTLB pressure, the driver may proceed with invalid > DMA addresses, potentially causing hardware errors, data corruption, or > system instability. > > Additionally, if mapping fails midway through processing fragmented > packets,previously mapped DMA resources are not released, leading > to DMA resource leaks. > > Fix this by: > 1. Checking dma_mapping_error() after each DMA mapping call. > 2. Implementing an error handling path to unmap successfully > mapped buffers(both linear and fragments) using > dma_unmap_single(). > 3. Freeing the skb using dev_kfree_skb_any() to safely handle > both process and softirq contexts, as hard_start_xmit may be > called with IRQs enabled. > 4. Returning NETDEV_TX_OK to drop the packet gracefully and > prevent TX queue stagnation. > > This ensures compliance with the DMA API guidelines and > improves driver stability under memory pressure. > > Fixes: fd9e4d6fec15 ("natsemi: switch from 'pci_' to 'dma_' API") The fix tag looks wrong, as the above just to mechanical substitution of used APIs. The issue is pre-existent > Cc: stable@vger.kernel.org > Signed-off-by: Wang Jun <1742789905@qq.com> > --- > drivers/net/ethernet/natsemi/ns83820.c | 32 ++++++++++++++++++++++++++ > 1 file changed, 32 insertions(+) > > diff --git a/drivers/net/ethernet/natsemi/ns83820.c b/drivers/net/ethernet/natsemi/ns83820.c > index cdbf82affa7b..90465e4977c3 100644 > --- a/drivers/net/ethernet/natsemi/ns83820.c > +++ b/drivers/net/ethernet/natsemi/ns83820.c > @@ -1051,6 +1051,12 @@ static netdev_tx_t ns83820_hard_start_xmit(struct sk_buff *skb, > int stopped = 0; > int do_intr = 0; > volatile __le32 *first_desc; > + dma_addr_t frag_dma_addr[MAX_SKB_FRAGS]; > + unsigned int frag_dma_len[MAX_SKB_FRAGS]; > + int frag_mapped_count = 0; > + dma_addr_t main_buf = 0; > + unsigned int main_len = 0; > + int i; Please respect the reverse christmas tree order above. > dprintk("ns83820_hard_start_xmit\n"); > > @@ -1121,6 +1127,13 @@ static netdev_tx_t ns83820_hard_start_xmit(struct sk_buff *skb, > buf = dma_map_single(&dev->pci_dev->dev, skb->data, len, > DMA_TO_DEVICE); > > + if (dma_mapping_error(&dev->pci_dev->dev, buf)) { > + dev_kfree_skb_any(skb); > + return NETDEV_TX_OK; > + } > + main_buf = buf; > + main_len = len; > + > first_desc = dev->tx_descs + (free_idx * DESC_SIZE); > > for (;;) { > @@ -1144,6 +1157,15 @@ static netdev_tx_t ns83820_hard_start_xmit(struct sk_buff *skb, > > buf = skb_frag_dma_map(&dev->pci_dev->dev, frag, 0, > skb_frag_size(frag), DMA_TO_DEVICE); > + if (dma_mapping_error(&dev->pci_dev->dev, buf)) > + goto dma_map_error; > + > + if (frag_mapped_count < MAX_SKB_FRAGS) { > + frag_dma_addr[frag_mapped_count] = buf; > + frag_dma_len[frag_mapped_count] = skb_frag_size(frag); > + frag_mapped_count++; > + } > + > dprintk("frag: buf=%08Lx page=%08lx offset=%08lx\n", > (long long)buf, (long) page_to_pfn(frag->page), > frag->page_offset); > @@ -1166,6 +1188,16 @@ static netdev_tx_t ns83820_hard_start_xmit(struct sk_buff *skb, > if (stopped && (dev->tx_done_idx != tx_done_idx) && start_tx_okay(dev)) > netif_start_queue(ndev); > > + return NETDEV_TX_OK; > +dma_map_error: > + dma_unmap_single(&dev->pci_dev->dev, main_buf, main_len, DMA_TO_DEVICE); > + for (i = 0; i < frag_mapped_count; i++) { > + dma_unmap_single(&dev->pci_dev->dev, frag_dma_addr[i], frag_dma_len[i], > + DMA_TO_DEVICE); > + } > + > + dev_kfree_skb_any(skb); AI review says: If nr_free < MIN_TX_DESC_FREE earlier in the function, netif_stop_queue is called and the stopped flag is set to 1. By returning NETDEV_TX_OK directly from the error path, we skip the race check at the end of the normal flow: if (stopped && (dev->tx_done_idx != tx_done_idx) && start_tx_okay(dev)) netif_start_queue(ndev); If all pending packets completed concurrently right before the queue was stopped, could this cause the TX queue to stall indefinitely until the tx watchdog fires?