netdev - Re: [PATCH net] virtio-net: suppress bad irq warning for tx napi

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Message-ID: <20210201182404.4ac54542@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 1 Feb 2021 18:24:04 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>
Cc:     Wei Wang <weiwan@...gle.com>, David Miller <davem@...emloft.net>,
        netdev@...r.kernel.org, Willem de Bruijn <willemb@...gle.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net] virtio-net: suppress bad irq warning for tx napi

On Thu, 28 Jan 2021 16:21:36 -0800 Wei Wang wrote:
> With the implementation of napi-tx in virtio driver, we clean tx
> descriptors from rx napi handler, for the purpose of reducing tx
> complete interrupts. But this could introduce a race where tx complete
> interrupt has been raised, but the handler found there is no work to do
> because we have done the work in the previous rx interrupt handler.
> This could lead to the following warning msg:
> [ 3588.010778] irq 38: nobody cared (try booting with the
> "irqpoll" option)
> [ 3588.017938] CPU: 4 PID: 0 Comm: swapper/4 Not tainted
> 5.3.0-19-generic #20~18.04.2-Ubuntu
> [ 3588.017940] Call Trace:
> [ 3588.017942]  <IRQ>
> [ 3588.017951]  dump_stack+0x63/0x85
> [ 3588.017953]  __report_bad_irq+0x35/0xc0
> [ 3588.017955]  note_interrupt+0x24b/0x2a0
> [ 3588.017956]  handle_irq_event_percpu+0x54/0x80
> [ 3588.017957]  handle_irq_event+0x3b/0x60
> [ 3588.017958]  handle_edge_irq+0x83/0x1a0
> [ 3588.017961]  handle_irq+0x20/0x30
> [ 3588.017964]  do_IRQ+0x50/0xe0
> [ 3588.017966]  common_interrupt+0xf/0xf
> [ 3588.017966]  </IRQ>
> [ 3588.017989] handlers:
> [ 3588.020374] [<000000001b9f1da8>] vring_interrupt
> [ 3588.025099] Disabling IRQ #38
> 
> This patch adds a new param to struct vring_virtqueue, and we set it for
> tx virtqueues if napi-tx is enabled, to suppress the warning in such
> case.
> 
> Fixes: 7b0411ef4aa6 ("virtio-net: clean tx descriptors from rx napi")
> Reported-by: Rick Jones <jonesrick@...gle.com>
> Signed-off-by: Wei Wang <weiwan@...gle.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

Michael, Jason, does this one look okay to you?