Re: [PATCH v4 1/2] rtw88: pci: Rearrange the memory usage for skb in RX ISR

[Jian-Hong Pan <jian-hong@endlessm.com>]

Jian-Hong Pan <jian-hong@endlessm.com> 於 2019年7月11日 週四 下午1:25寫道：
>
> 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, to fixing the kernel crash, the RX routine should now
> generally behave better under low memory conditions.
>
> Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=204053
> Signed-off-by: Jian-Hong Pan <jian-hong@endlessm.com>
> Cc: <stable@vger.kernel.org>
> ---

Sorry, I forget to place the version difference here.

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.

v4:
 - Fix comment: allocate a new skb for this frame, discard the frame
if none available

>  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..c415f5e94fed 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);
> +               /* allocate a new skb for this frame,
> +                * discard the frame 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"))
> +                       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
>