netdev - Re: [PATCH bpf 0/3] XSK related fixes

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Date:   Wed, 5 Feb 2020 22:21:47 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc:     ast@...nel.org, netdev@...r.kernel.org, bpf@...r.kernel.org,
        bjorn.topel@...el.com, magnus.karlsson@...el.com,
        maximmi@...lanox.com
Subject: Re: [PATCH bpf 0/3] XSK related fixes

On Wed, Feb 05, 2020 at 05:58:31AM +0100, Maciej Fijalkowski wrote:
> Cameron reported [0] that on fresh bpf-next he could not run multiple
> xdpsock instances in Tx-only mode on single network interface with i40e
> driver.
> 
> Turns out that Maxim's series [1] which was adding RCU protection around
> ndo_xsk_wakeup added check against the __I40E_CONFIG_BUSY being set on
> pf->state within i40e_xsk_wakeup() - if it's set, return -ENETDOWN.
> Since this bit is set per PF when UMEM is being enabled/disabled, the
> situation Cameron stumbled upon was that when he launched second xdpsock
> instance, second UMEM was being registered, hence set __I40E_CONFIG_BUSY
> which is now observed by first xdpsock and therefore xdpsock's kick_tx()
> gets -ENETDOWN as errno.
> 
> -ENETDOWN currently is not allowed in kick_tx(), so we were exiting the
> first application. Such exit means also XDP program being unloaded and
> its dedicated resources, which caused an -ENXIO being return in the
> second xdpsock instance.
> 
> Let's fix the issue from both sides - protect ourselves from future
> xdpsock crashes by allowing for -ENETDOWN errno being set in kick_tx()
> (patch 3) and from driver side, return -EAGAIN for the case where PF is
> busy (patch 1).
> 
> Remove also doubled variable from xdpsock_user.c (patch 2).
> 
> Note that ixgbe seems not to be affected since UMEM registration sets
> the busy/disable bit per ring, not per PF.
> 
> Thanks!
> Maciej
> 
> [0]: https://www.spinics.net/lists/xdp-newbies/msg01558.html
> [1]: https://lore.kernel.org/netdev/20191217162023.16011-1-maximmi@mellanox.com/

Applied, thanks!