Message-ID: <CACGkMEuCO0xBB9cDxp=fpZTMjCLcCdzQP+5_LysuDbWV4Ru1Lw@mail.gmail.com>
Date: Mon, 2 Dec 2024 12:22:30 +0800
From: Jason Wang <jasowang@...hat.com>
To: Koichiro Den <koichiro.den@...onical.com>
Cc: virtualization@...ts.linux.dev, mst@...hat.com, xuanzhuo@...ux.alibaba.com, 
	eperezma@...hat.com, andrew+netdev@...n.ch, davem@...emloft.net, 
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] virtio_net: drain unconsumed tx completions if any before dql_reset

On Sat, Nov 30, 2024 at 11:18 PM Koichiro Den
<koichiro.den@...onical.com> wrote:
>
> On Fri, Nov 29, 2024 at 10:18:04AM +0800, Jason Wang wrote:
> > On Thu, Nov 28, 2024 at 12:25 PM Koichiro Den
> > <koichiro.den@...onical.com> wrote:
> > >
> > > On Thu, Nov 28, 2024 at 10:57:01AM +0800, Jason Wang wrote:
> > > > On Wed, Nov 27, 2024 at 12:08 PM Koichiro Den
> > > > <koichiro.den@...onical.com> wrote:
> > > > >
> > > > > On Wed, Nov 27, 2024 at 11:24:15AM +0800, Jason Wang wrote:
> > > > > > On Tue, Nov 26, 2024 at 12:44 PM Koichiro Den
> > > > > > <koichiro.den@...onical.com> wrote:
> > > > > > >
> > > > > > > On Tue, Nov 26, 2024 at 11:50:17AM +0800, Jason Wang wrote:
> > > > > > > > On Tue, Nov 26, 2024 at 10:42 AM Koichiro Den
> > > > > > > > <koichiro.den@...onical.com> wrote:
> > > > > > > > >
> > > > > > > > > When virtnet_close is followed by virtnet_open, there is a slight chance
> > > > > > > > > that some TX completions remain unconsumed. Those are handled during the
> > > > > > > > > first NAPI poll, but since dql_reset occurs just beforehand, it can lead
> > > > > > > > > to a crash [1].
> > > > > > > > >
> > > > > > > > > This issue can be reproduced by running: `while :; do ip l set DEV down;
> > > > > > > > > ip l set DEV up; done` under heavy network TX load from inside of the
> > > > > > > > > machine.
> > > > > > > > >
> > > > > > > > > To fix this, drain unconsumed TX completions if any before dql_reset,
> > > > > > > > > allowing BQL to start cleanly.
> > > > > > > > >
> > > > > > > > > ------------[ cut here ]------------
> > > > > > > > > kernel BUG at lib/dynamic_queue_limits.c:99!
> > > > > > > > > Oops: invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
> > > > > > > > > CPU: 7 UID: 0 PID: 1598 Comm: ip Tainted: G    N 6.12.0net-next_main+ #2
> > > > > > > > > Tainted: [N]=TEST
> > > > > > > > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), \
> > > > > > > > > BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
> > > > > > > > > RIP: 0010:dql_completed+0x26b/0x290
> > > > > > > > > Code: b7 c2 49 89 e9 44 89 da 89 c6 4c 89 d7 e8 ed 17 47 00 58 65 ff 0d
> > > > > > > > > 4d 27 90 7e 0f 85 fd fe ff ff e8 ea 53 8d ff e9 f3 fe ff ff <0f> 0b 01
> > > > > > > > > d2 44 89 d1 29 d1 ba 00 00 00 00 0f 48 ca e9 28 ff ff ff
> > > > > > > > > RSP: 0018:ffffc900002b0d08 EFLAGS: 00010297
> > > > > > > > > RAX: 0000000000000000 RBX: ffff888102398c80 RCX: 0000000080190009
> > > > > > > > > RDX: 0000000000000000 RSI: 000000000000006a RDI: 0000000000000000
> > > > > > > > > RBP: ffff888102398c00 R08: 0000000000000000 R09: 0000000000000000
> > > > > > > > > R10: 00000000000000ca R11: 0000000000015681 R12: 0000000000000001
> > > > > > > > > R13: ffffc900002b0d68 R14: ffff88811115e000 R15: ffff8881107aca40
> > > > > > > > > FS:  00007f41ded69500(0000) GS:ffff888667dc0000(0000)
> > > > > > > > > knlGS:0000000000000000
> > > > > > > > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > > > > > > > CR2: 0000556ccc2dc1a0 CR3: 0000000104fd8003 CR4: 0000000000772ef0
> > > > > > > > > PKRU: 55555554
> > > > > > > > > Call Trace:
> > > > > > > > >  <IRQ>
> > > > > > > > >  ? die+0x32/0x80
> > > > > > > > >  ? do_trap+0xd9/0x100
> > > > > > > > >  ? dql_completed+0x26b/0x290
> > > > > > > > >  ? dql_completed+0x26b/0x290
> > > > > > > > >  ? do_error_trap+0x6d/0xb0
> > > > > > > > >  ? dql_completed+0x26b/0x290
> > > > > > > > >  ? exc_invalid_op+0x4c/0x60
> > > > > > > > >  ? dql_completed+0x26b/0x290
> > > > > > > > >  ? asm_exc_invalid_op+0x16/0x20
> > > > > > > > >  ? dql_completed+0x26b/0x290
> > > > > > > > >  __free_old_xmit+0xff/0x170 [virtio_net]
> > > > > > > > >  free_old_xmit+0x54/0xc0 [virtio_net]
> > > > > > > > >  virtnet_poll+0xf4/0xe30 [virtio_net]
> > > > > > > > >  ? __update_load_avg_cfs_rq+0x264/0x2d0
> > > > > > > > >  ? update_curr+0x35/0x260
> > > > > > > > >  ? reweight_entity+0x1be/0x260
> > > > > > > > >  __napi_poll.constprop.0+0x28/0x1c0
> > > > > > > > >  net_rx_action+0x329/0x420
> > > > > > > > >  ? enqueue_hrtimer+0x35/0x90
> > > > > > > > >  ? trace_hardirqs_on+0x1d/0x80
> > > > > > > > >  ? kvm_sched_clock_read+0xd/0x20
> > > > > > > > >  ? sched_clock+0xc/0x30
> > > > > > > > >  ? kvm_sched_clock_read+0xd/0x20
> > > > > > > > >  ? sched_clock+0xc/0x30
> > > > > > > > >  ? sched_clock_cpu+0xd/0x1a0
> > > > > > > > >  handle_softirqs+0x138/0x3e0
> > > > > > > > >  do_softirq.part.0+0x89/0xc0
> > > > > > > > >  </IRQ>
> > > > > > > > >  <TASK>
> > > > > > > > >  __local_bh_enable_ip+0xa7/0xb0
> > > > > > > > >  virtnet_open+0xc8/0x310 [virtio_net]
> > > > > > > > >  __dev_open+0xfa/0x1b0
> > > > > > > > >  __dev_change_flags+0x1de/0x250
> > > > > > > > >  dev_change_flags+0x22/0x60
> > > > > > > > >  do_setlink.isra.0+0x2df/0x10b0
> > > > > > > > >  ? rtnetlink_rcv_msg+0x34f/0x3f0
> > > > > > > > >  ? netlink_rcv_skb+0x54/0x100
> > > > > > > > >  ? netlink_unicast+0x23e/0x390
> > > > > > > > >  ? netlink_sendmsg+0x21e/0x490
> > > > > > > > >  ? ____sys_sendmsg+0x31b/0x350
> > > > > > > > >  ? avc_has_perm_noaudit+0x67/0xf0
> > > > > > > > >  ? cred_has_capability.isra.0+0x75/0x110
> > > > > > > > >  ? __nla_validate_parse+0x5f/0xee0
> > > > > > > > >  ? __pfx___probestub_irq_enable+0x3/0x10
> > > > > > > > >  ? __create_object+0x5e/0x90
> > > > > > > > >  ? security_capable+0x3b/0x70
> > > > > > > > >  rtnl_newlink+0x784/0xaf0
> > > > > > > > >  ? avc_has_perm_noaudit+0x67/0xf0
> > > > > > > > >  ? cred_has_capability.isra.0+0x75/0x110
> > > > > > > > >  ? stack_depot_save_flags+0x24/0x6d0
> > > > > > > > >  ? __pfx_rtnl_newlink+0x10/0x10
> > > > > > > > >  rtnetlink_rcv_msg+0x34f/0x3f0
> > > > > > > > >  ? do_syscall_64+0x6c/0x180
> > > > > > > > >  ? entry_SYSCALL_64_after_hwframe+0x76/0x7e
> > > > > > > > >  ? __pfx_rtnetlink_rcv_msg+0x10/0x10
> > > > > > > > >  netlink_rcv_skb+0x54/0x100
> > > > > > > > >  netlink_unicast+0x23e/0x390
> > > > > > > > >  netlink_sendmsg+0x21e/0x490
> > > > > > > > >  ____sys_sendmsg+0x31b/0x350
> > > > > > > > >  ? copy_msghdr_from_user+0x6d/0xa0
> > > > > > > > >  ___sys_sendmsg+0x86/0xd0
> > > > > > > > >  ? __pte_offset_map+0x17/0x160
> > > > > > > > >  ? preempt_count_add+0x69/0xa0
> > > > > > > > >  ? __call_rcu_common.constprop.0+0x147/0x610
> > > > > > > > >  ? preempt_count_add+0x69/0xa0
> > > > > > > > >  ? preempt_count_add+0x69/0xa0
> > > > > > > > >  ? _raw_spin_trylock+0x13/0x60
> > > > > > > > >  ? trace_hardirqs_on+0x1d/0x80
> > > > > > > > >  __sys_sendmsg+0x66/0xc0
> > > > > > > > >  do_syscall_64+0x6c/0x180
> > > > > > > > >  entry_SYSCALL_64_after_hwframe+0x76/0x7e
> > > > > > > > > RIP: 0033:0x7f41defe5b34
> > > > > > > > > Code: 15 e1 12 0f 00 f7 d8 64 89 02 b8 ff ff ff ff eb bf 0f 1f 44 00 00
> > > > > > > > > f3 0f 1e fa 80 3d 35 95 0f 00 00 74 13 b8 2e 00 00 00 0f 05 <48> 3d 00
> > > > > > > > > f0 ff ff 77 4c c3 0f 1f 00 55 48 89 e5 48 83 ec 20 89 55
> > > > > > > > > RSP: 002b:00007ffe5336ecc8 EFLAGS: 00000202 ORIG_RAX: 000000000000002e
> > > > > > > > > RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f41defe5b34
> > > > > > > > > RDX: 0000000000000000 RSI: 00007ffe5336ed30 RDI: 0000000000000003
> > > > > > > > > RBP: 00007ffe5336eda0 R08: 0000000000000010 R09: 0000000000000001
> > > > > > > > > R10: 00007ffe5336f6f9 R11: 0000000000000202 R12: 0000000000000003
> > > > > > > > > R13: 0000000067452259 R14: 0000556ccc28b040 R15: 0000000000000000
> > > > > > > > >  </TASK>
> > > > > > > > > [...]
> > > > > > > > > ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---
> > > > > > > > >
> > > > > > > > > Fixes: c8bd1f7f3e61 ("virtio_net: add support for Byte Queue Limits")
> > > > > > > > > Cc: <stable@...r.kernel.org> # v6.11+
> > > > > > > > > Signed-off-by: Koichiro Den <koichiro.den@...onical.com>
> > > > > > > > > ---
> > > > > > > > >  drivers/net/virtio_net.c | 37 +++++++++++++++++++++++++++++--------
> > > > > > > > >  1 file changed, 29 insertions(+), 8 deletions(-)
> > > > > > > > >
> > > > > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > > > > > > index 64c87bb48a41..3e36c0470600 100644
> > > > > > > > > --- a/drivers/net/virtio_net.c
> > > > > > > > > +++ b/drivers/net/virtio_net.c
> > > > > > > > > @@ -513,7 +513,7 @@ static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
> > > > > > > > >                                                struct sk_buff *curr_skb,
> > > > > > > > >                                                struct page *page, void *buf,
> > > > > > > > >                                                int len, int truesize);
> > > > > > > > > -static void virtnet_xsk_completed(struct send_queue *sq, int num);
> > > > > > > > > +static void virtnet_xsk_completed(struct send_queue *sq, int num, bool drain);
> > > > > > > > >
> > > > > > > > >  enum virtnet_xmit_type {
> > > > > > > > >         VIRTNET_XMIT_TYPE_SKB,
> > > > > > > > > @@ -580,7 +580,8 @@ static void sg_fill_dma(struct scatterlist *sg, dma_addr_t addr, u32 len)
> > > > > > > > >  }
> > > > > > > > >
> > > > > > > > >  static void __free_old_xmit(struct send_queue *sq, struct netdev_queue *txq,
> > > > > > > > > -                           bool in_napi, struct virtnet_sq_free_stats *stats)
> > > > > > > > > +                           bool in_napi, struct virtnet_sq_free_stats *stats,
> > > > > > > > > +                           bool drain)
> > > > > > > > >  {
> > > > > > > > >         struct xdp_frame *frame;
> > > > > > > > >         struct sk_buff *skb;
> > > > > > > > > @@ -620,7 +621,8 @@ static void __free_old_xmit(struct send_queue *sq, struct netdev_queue *txq,
> > > > > > > > >                         break;
> > > > > > > > >                 }
> > > > > > > > >         }
> > > > > > > > > -       netdev_tx_completed_queue(txq, stats->napi_packets, stats->napi_bytes);
> > > > > > > > > +       if (!drain)
> > > > > > > > > +               netdev_tx_completed_queue(txq, stats->napi_packets, stats->napi_bytes);
> > > > > > > > >  }
> > > > > > > > >
> > > > > > > > >  static void virtnet_free_old_xmit(struct send_queue *sq,
> > > > > > > > > @@ -628,10 +630,21 @@ static void virtnet_free_old_xmit(struct send_queue *sq,
> > > > > > > > >                                   bool in_napi,
> > > > > > > > >                                   struct virtnet_sq_free_stats *stats)
> > > > > > > > >  {
> > > > > > > > > -       __free_old_xmit(sq, txq, in_napi, stats);
> > > > > > > > > +       __free_old_xmit(sq, txq, in_napi, stats, false);
> > > > > > > > >
> > > > > > > > >         if (stats->xsk)
> > > > > > > > > -               virtnet_xsk_completed(sq, stats->xsk);
> > > > > > > > > +               virtnet_xsk_completed(sq, stats->xsk, false);
> > > > > > > > > +}
> > > > > > > > > +
> > > > > > > > > +static void virtnet_drain_old_xmit(struct send_queue *sq,
> > > > > > > > > +                                  struct netdev_queue *txq)
> > > > > > > > > +{
> > > > > > > > > +       struct virtnet_sq_free_stats stats = {0};
> > > > > > > > > +
> > > > > > > > > +       __free_old_xmit(sq, txq, false, &stats, true);
> > > > > > > > > +
> > > > > > > > > +       if (stats.xsk)
> > > > > > > > > +               virtnet_xsk_completed(sq, stats.xsk, true);
> > > > > > > > >  }
> > > > > > > >
> > > > > > > > Are we sure this can drain the queue? Note that the device is not stopped.
> > > > > > >
> > > > > > > Thanks for reviewing. netif_tx_wake_queue can be invoked before the "drain"
> > > > > > > point I added e.g. via virtnet_config_changed_work, so it seems that I need
> > > > > > > to ensure it's stopped (DRV_XOFF) before the "drain" and wake it afterwards.
> > > > > > > Please let me know if I’m mistaken.
> > > > > >
> > > > > > Not sure I get you, but I meant we don't reset the device so it can
> > > > >
> > > > > I was wondering whether there would be a scenario where the tx queue is
> > > > > woken up and some new packets from the upper layer reach dql_queued()
> > > > > before the drain point, which also could cause the crash.
> > > >
> > > > Ok.
> > > >
> > > > >
> > > > > > keep raising tx interrupts:
> > > > > >
> > > > > > virtnet_drain_old_xmit()
> > > > > > netdev_tx_reset_queue()
> > > > > > skb_xmit_done()
> > > > > > napi_enable()
> > > > > > netdev_tx_completed_queue() // here we might still surprise the bql?
> > > > >
> > > > > Indeed, virtqueue_disable_cb() is needed before the drain point.
> > > >
> > > > Two problems:
> > > >
> > > > 1) device/virtqueue is not reset, it can still process the packets
> > > > after virtnet_drain_old_xmit()
> > > > 2) virtqueue_disable_cb() just does its best effort, it can't
> > > > guarantee no interrupt after that.
> > > >
> > > > To drain TX, the only reliable seems to be:
> > > >
> > > > 1) reset a virtqueue (or a device)
> > > > 2) drain by using free_old_xmit()
> > > > 3) netif_reset_tx_queue() // btw this seems to be better done in close not open
> > >
> > > Thank you for the clarification.
> > > As for 1), I may be missing something but what if VIRTIO_F_RING_RESET is
> > > not supported. A device reset in this context feels a bit excessive to me
> > > (just my two cents though) if in virtnet_open, so as you said, it seems
> > > better done in close in that regard as well.
> >
> > Probably, most NIC has a way to stop its TX which is missed in
> > virtio-net. So we don't have more choices other than device reset when
> > there's no virtqueue reset.
> >
> > Or we can limit the BQL to virtqueue reset, AF_XDP used to suffer from
> > the exact issue when there's no virtqueue reset. That's why virtqueue
> > reset is invented and AF_XDP is limited to virtqueue reset.
>
> Thank you for the response.
>
> Hmm, if we do a device reset, to me it seems better to (re-)initialize the
> device in a sane way (i.e. ACKNOWLEDGE->DRIVER->...->DRIVER_OK) here as
> well, to avoid potentially surprising the hyperviour side, IIUC. That would
> essentially make it nearly equivalent to the current freeze/restore
> handling. However, performing such a reset in open or close path would
> likely require a fundamental restructuring/redefinition of the open/close
> semantics for virtio-net, right? Otherwise I guess it would be a dirty hack
> solely for this BQL issue. Limitting the BQL to virtqueue reset sounds
> nicer, but I'm now inclined to your suggestion to simply drop
> netdev_tx_reset_queue(), as mentioned in my response below.

Right.

>
> >
> > >
> > > >
> > > > Or I wonder if this can be easily fixed by just removing
> > > > netdev_tx_reset_queue()?
> > >
> > > Perhaps introducing a variant of dql_reset() that clears all stall history
> > > would suffice? To avoid excessively long stall_max to be possibly recorded.
> >
> > Not sure, it looks like the problem still, bql might still be
> > surprised when it might get completed tx packets when it think it
> > hasn't sent any?
>
> I meant an API that would clear only stall_max, without requiring users to
> do so in such cases. That said, I just noticed that commit message of
> 6025b9135f7a ("net: dqs: add NIC stall detector based on BQL") mentions
> that "this mechanism does not ignore stalls caused by Tx being disabled, or
> loss of link", primarily for simplicity's sake. Given this, simply dropping
> netdev_tx_reset_queue() seems like a streamlined approach. I'll resend a
> patch that does so. If I'm missing something or mistaken, please let me
> know.

I think we can go this way. So I will ACK that patch.

Thanks

>
> Thanks
>
> >
> > Thanks
> >
> > >
> > > Thanks
> > >
> > > >
> > > > Thanks
> > > >
> > > > >
> > > > > Thanks
> > > > >
> > > > > >
> > > > > > Thanks
> > > > > >
> > > > > > >
> > > > > > > >
> > > > > > > > >
> > > > > > > > >  /* Converting between virtqueue no. and kernel tx/rx queue no.
> > > > > > > > > @@ -1499,7 +1512,8 @@ static bool virtnet_xsk_xmit(struct send_queue *sq, struct xsk_buff_pool *pool,
> > > > > > > > >         /* Avoid to wakeup napi meanless, so call __free_old_xmit instead of
> > > > > > > > >          * free_old_xmit().
> > > > > > > > >          */
> > > > > > > > > -       __free_old_xmit(sq, netdev_get_tx_queue(dev, sq - vi->sq), true, &stats);
> > > > > > > > > +       __free_old_xmit(sq, netdev_get_tx_queue(dev, sq - vi->sq), true,
> > > > > > > > > +                       &stats, false);
> > > > > > > > >
> > > > > > > > >         if (stats.xsk)
> > > > > > > > >                 xsk_tx_completed(sq->xsk_pool, stats.xsk);
> > > > > > > > > @@ -1556,10 +1570,13 @@ static int virtnet_xsk_wakeup(struct net_device *dev, u32 qid, u32 flag)
> > > > > > > > >         return 0;
> > > > > > > > >  }
> > > > > > > > >
> > > > > > > > > -static void virtnet_xsk_completed(struct send_queue *sq, int num)
> > > > > > > > > +static void virtnet_xsk_completed(struct send_queue *sq, int num, bool drain)
> > > > > > > > >  {
> > > > > > > > >         xsk_tx_completed(sq->xsk_pool, num);
> > > > > > > > >
> > > > > > > > > +       if (drain)
> > > > > > > > > +               return;
> > > > > > > > > +
> > > > > > > > >         /* If this is called by rx poll, start_xmit and xdp xmit we should
> > > > > > > > >          * wakeup the tx napi to consume the xsk tx queue, because the tx
> > > > > > > > >          * interrupt may not be triggered.
> > > > > > > > > @@ -3041,6 +3058,7 @@ static void virtnet_disable_queue_pair(struct virtnet_info *vi, int qp_index)
> > > > > > > > >
> > > > > > > > >  static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index)
> > > > > > > > >  {
> > > > > > > > > +       struct netdev_queue *txq = netdev_get_tx_queue(vi->dev, qp_index);
> > > > > > > > >         struct net_device *dev = vi->dev;
> > > > > > > > >         int err;
> > > > > > > > >
> > > > > > > > > @@ -3054,7 +3072,10 @@ static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index)
> > > > > > > > >         if (err < 0)
> > > > > > > > >                 goto err_xdp_reg_mem_model;
> > > > > > > > >
> > > > > > > > > -       netdev_tx_reset_queue(netdev_get_tx_queue(vi->dev, qp_index));
> > > > > > > > > +       /* Drain any unconsumed TX skbs transmitted before the last virtnet_close */
> > > > > > > > > +       virtnet_drain_old_xmit(&vi->sq[qp_index], txq);
> > > > > > > > > +
> > > > > > > > > +       netdev_tx_reset_queue(txq);
> > > > > > > > >         virtnet_napi_enable(vi->rq[qp_index].vq, &vi->rq[qp_index].napi);
> > > > > > > > >         virtnet_napi_tx_enable(vi, vi->sq[qp_index].vq, &vi->sq[qp_index].napi);
> > > > > > > > >
> > > > > > > > > --
> > > > > > > > > 2.43.0
> > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > > > Thanks
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

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