Messages in this thread | | | Date | Fri, 20 Aug 2021 18:09:48 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH net-next] stmmac: align RX buffers |
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On Fri, 20 Aug 2021 17:38:14 +0100, Matteo Croce <mcroce@linux.microsoft.com> wrote: > > On Fri, Aug 20, 2021 at 6:26 PM Marc Zyngier <maz@kernel.org> wrote: > > > > On Fri, 20 Aug 2021 11:37:03 +0100, > > Matteo Croce <mcroce@linux.microsoft.com> wrote: > > > > > > On Thu, Aug 19, 2021 at 6:29 PM Marc Zyngier <maz@kernel.org> wrote: > > > > [...] > > > > > > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h > > > > index fcdb1d20389b..244aa6579ef4 100644 > > > > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h > > > > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h > > > > @@ -341,7 +341,7 @@ static inline unsigned int stmmac_rx_offset(struct stmmac_priv *priv) > > > > if (stmmac_xdp_is_enabled(priv)) > > > > return XDP_PACKET_HEADROOM + NET_IP_ALIGN; > > > > > > > > - return NET_SKB_PAD + NET_IP_ALIGN; > > > > + return 8 + NET_IP_ALIGN; > > > > } > > > > > > > > void stmmac_disable_rx_queue(struct stmmac_priv *priv, u32 queue); > > > > > > > > I don't see the system corrupting packets anymore. Is that exactly > > > > what you had in mind? This really seems to point to a basic buffer > > > > overflow. > > > > [...] > > > > > Sorry, I meant something like: > > > > > > - return NET_SKB_PAD + NET_IP_ALIGN; > > > + return 8; > > > > > > I had some hardware which DMA fails if the receive buffer was not word > > > aligned, but this seems not the case, as 8 + NET_IP_ALIGN = 10, and > > > it's not aligned too. > > > > No error in that case either, as expected. Given that NET_SKB_PAD is > > likely to expand to 64, it is likely a DMA buffer overflow which > > probably only triggers for large-ish packets. > > > > Now, we're almost at -rc7, and we don't have a solution in sight. > > > > Can we please revert this until we have an understanding of what is > > happening? I'll hopefully have more cycles to work on the issue once > > 5.14 is out, and hopefully the maintainers of this driver can chime in > > (they have been pretty quiet so far). > > > > Thanks, > > > > M. > > > > -- > > Without deviation from the norm, progress is not possible. > > Last try, what about adding only NET_IP_ALIGN and leaving NET_SKB_PAD? > > - return NET_SKB_PAD + NET_IP_ALIGN; > + return NET_IP_ALIGN; > > I think that alloc_skb adds another NET_SKB_PAD anyway.
I don't see any packet corruption with this. However, this doesn't prove that this is correct either. What was the rational for adding NET_SKB_PAD the first place?
M.
-- Without deviation from the norm, progress is not possible.
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