Re: [PATCH v2 1/2] rtw88: pci: Rearrange the memory usage for skb in RX ISR

From: Jian-Hong Pan
Date: Wed Jul 10 2019 - 04:55:09 EST

Tony Chuang <yhchuang@xxxxxxxxxxx> æ 2019å7æ10æ éä äå4:37åéï
>
> > Subject: [PATCH v2 1/2] rtw88: pci: Rearrange the memory usage for skb in
> > RX ISR
> >
> > 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@xxxxxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > ---
> > 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
> > + */
> > + 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
>
> Now it looks good to me. Thanks.
>
> Acked-by: Yan-Hsuan Chuang <yhchuang@xxxxxxxxxxx>
>
> Yan-Hsuan

Uh! Thanks for your ack.
But I just sent version 3 patches (including [PATCH v3 2/2] rtw88:
pci: Use DMA sync instead of remapping in RX ISR) by following
Christoph's comment. [1]

Could you please also review the 2 patches of version 3? Thank you.

[1]: https://lkml.org/lkml/2019/7/9/507

Jian-Hong Pan