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Date: Wed, 10 Jul 2019 08:57:06 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Jian-Hong Pan' <jian-hong@...lessm.com>,
Yan-Hsuan Chuang <yhchuang@...ltek.com>,
Kalle Valo <kvalo@...eaurora.org>,
"David S . Miller" <davem@...emloft.net>,
Larry Finger <Larry.Finger@...inger.net>,
"Christoph Hellwig" <hch@...radead.org>
CC: "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux@...lessm.com" <linux@...lessm.com>,
Daniel Drake <drake@...lessm.com>,
"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH v3 1/2] rtw88: pci: Rearrange the memory usage for skb in
RX ISR
From: Jian-Hong Pan
> Sent: 10 July 2019 09:38
>
> Testing with RTL8822BE hardware, when available memory is low, we
> frequently see a kernel panic and system freeze.
>
> First, rtw_pci_rx_isr encounters a memory allocation failure (trimmed):
>
> rx routine starvation
> WARNING: CPU: 7 PID: 9871 at drivers/net/wireless/realtek/rtw88/pci.c:822
> rtw_pci_rx_isr.constprop.25+0x35a/0x370 [rtwpci]
> [ 2356.580313] RIP: 0010:rtw_pci_rx_isr.constprop.25+0x35a/0x370 [rtwpci]
>
> Then we see a variety of different error conditions and kernel panics,
> such as this one (trimmed):
>
> rtw_pci 0000:02:00.0: pci bus timeout, check dma status
> skbuff: skb_over_panic: text:00000000091b6e66 len:415 put:415 head:00000000d2880c6f
> data:000000007a02b1ea tail:0x1df end:0xc0 dev:<NULL>
> ------------[ cut here ]------------
> kernel BUG at net/core/skbuff.c:105!
> invalid opcode: 0000 [#1] SMP NOPTI
> RIP: 0010:skb_panic+0x43/0x45
>
> When skb allocation fails and the "rx routine starvation" is hit, the
> function returns immediately without updating the RX ring. At this
> point, the RX ring may continue referencing an old skb which was already
> handed off to ieee80211_rx_irqsafe(). When it comes to be used again,
> bad things happen.
>
> This patch allocates a new, data-sized skb first in RX ISR. After
> copying the data in, we pass it to the upper layers. However, if skb
> allocation fails, we effectively drop the frame. In both cases, the
> original, full size ring skb is reused.
>
> In addition, by fixing the kernel crash, the RX routine should now
> generally behave better under low memory conditions.
A couple of minor nits (see below).
You may want to do a followup patch that changes the rx buffers
(used by the hardware) to by just memory buffers.
Nothing (probably) relies on them being skb with all the accociated
baggage.
David
>
> Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=204053
> Signed-off-by: Jian-Hong Pan <jian-hong@...lessm.com>
> Cc: <stable@...r.kernel.org>
> ---
> v2:
> - Allocate new data-sized skb and put data into it, then pass it to
> mac80211. Reuse the original skb in RX ring by DMA sync.
> - Modify the commit message.
> - Introduce following [PATCH v3 2/2] rtw88: pci: Use DMA sync instead
> of remapping in RX ISR.
>
> v3:
> - Same as v2.
>
> drivers/net/wireless/realtek/rtw88/pci.c | 49 +++++++++++-------------
> 1 file changed, 22 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/net/wireless/realtek/rtw88/pci.c b/drivers/net/wireless/realtek/rtw88/pci.c
> index cfe05ba7280d..e9fe3ad896c8 100644
> --- a/drivers/net/wireless/realtek/rtw88/pci.c
> +++ b/drivers/net/wireless/realtek/rtw88/pci.c
> @@ -763,6 +763,7 @@ static void rtw_pci_rx_isr(struct rtw_dev *rtwdev, struct rtw_pci *rtwpci,
> u32 pkt_offset;
> u32 pkt_desc_sz = chip->rx_pkt_desc_sz;
> u32 buf_desc_sz = chip->rx_buf_desc_sz;
> + u32 new_len;
> u8 *rx_desc;
> dma_addr_t dma;
>
> @@ -790,40 +791,34 @@ static void rtw_pci_rx_isr(struct rtw_dev *rtwdev, struct rtw_pci *rtwpci,
> pkt_offset = pkt_desc_sz + pkt_stat.drv_info_sz +
> pkt_stat.shift;
>
> - if (pkt_stat.is_c2h) {
> - /* keep rx_desc, halmac needs it */
> - skb_put(skb, pkt_stat.pkt_len + pkt_offset);
> + /* discard current skb if the new skb cannot be allocated as a
> + * new one in rx ring later
> + */
That comment isn't quite right.
maybe: "Allocate a new skb for this frame, discard if none available"
> + new_len = pkt_stat.pkt_len + pkt_offset;
> + new = dev_alloc_skb(new_len);
> + if (WARN_ONCE(!new, "rx routine starvation\n"))
I think you should count these??
> + goto next_rp;
> +
> + /* put the DMA data including rx_desc from phy to new skb */
> + skb_put_data(new, skb->data, new_len);
>
> - /* pass offset for further operation */
> - *((u32 *)skb->cb) = pkt_offset;
> - skb_queue_tail(&rtwdev->c2h_queue, skb);
> + if (pkt_stat.is_c2h) {
> + /* pass rx_desc & offset for further operation */
> + *((u32 *)new->cb) = pkt_offset;
> + skb_queue_tail(&rtwdev->c2h_queue, new);
> ieee80211_queue_work(rtwdev->hw, &rtwdev->c2h_work);
> } else {
> - /* remove rx_desc, maybe use skb_pull? */
> - skb_put(skb, pkt_stat.pkt_len);
> - skb_reserve(skb, pkt_offset);
> -
> - /* alloc a smaller skb to mac80211 */
> - new = dev_alloc_skb(pkt_stat.pkt_len);
> - if (!new) {
> - new = skb;
> - } else {
> - skb_put_data(new, skb->data, skb->len);
> - dev_kfree_skb_any(skb);
> - }
> - /* TODO: merge into rx.c */
> - rtw_rx_stats(rtwdev, pkt_stat.vif, skb);
> + /* remove rx_desc */
> + skb_pull(new, pkt_offset);
> +
> + rtw_rx_stats(rtwdev, pkt_stat.vif, new);
> memcpy(new->cb, &rx_status, sizeof(rx_status));
> ieee80211_rx_irqsafe(rtwdev->hw, new);
> }
>
> - /* skb delivered to mac80211, alloc a new one in rx ring */
> - new = dev_alloc_skb(RTK_PCI_RX_BUF_SIZE);
> - if (WARN(!new, "rx routine starvation\n"))
> - return;
> -
> - ring->buf[cur_rp] = new;
> - rtw_pci_reset_rx_desc(rtwdev, new, ring, cur_rp, buf_desc_sz);
> +next_rp:
> + /* new skb delivered to mac80211, re-enable original skb DMA */
> + rtw_pci_reset_rx_desc(rtwdev, skb, ring, cur_rp, buf_desc_sz);
>
> /* host read next element in ring */
> if (++cur_rp >= ring->r.len)
> --
> 2.22.0
-
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