On Thu, Dec 05, 2024 at 05:33:36AM -0500, Michael S. Tsirkin wrote:
> On Wed, Dec 04, 2024 at 02:07:18PM +0900, Koichiro Den wrote:
> > When virtnet_close is followed by virtnet_open, some TX completions can
> > possibly remain unconsumed, until they are finally processed during the
> > first NAPI poll after the netdev_tx_reset_queue(), resulting in a crash
> > [1].
>
>
> So it's a bugfix. Why net-next not net?
I was mistaken (I just read netdev-FAQ again). I'll resend to net, with
adjustments reflecting your feedback.
>
> > Commit b96ed2c97c79 ("virtio_net: move netdev_tx_reset_queue() call
> > before RX napi enable") was not sufficient to eliminate all BQL crash
> > cases for virtio-net.
> >
> > This issue can be reproduced with the latest net-next master by running:
> > `while :; do ip l set DEV down; ip l set DEV up; done` under heavy network
> > TX load from inside the machine.
> >
> > netdev_tx_reset_queue() can actually be dropped from virtnet_open path;
> > the device is not stopped in any case. For BQL core part, it's just like
> > traffic nearly ceases to exist for some period. For stall detector added
> > to BQL, even if virtnet_close could somehow lead to some TX completions
> > delayed for long, followed by virtnet_open, we can just take it as stall
> > as mentioned in commit 6025b9135f7a ("net: dqs: add NIC stall detector
> > based on BQL"). Note also that users can still reset stall_max via sysfs.
> >
> > So, drop netdev_tx_reset_queue() from virtnet_enable_queue_pair(). This
> > eliminates the BQL crashes. Note that netdev_tx_reset_queue() is now
> > explicitly required in freeze/restore path, so this patch adds it to
> > free_unused_bufs().
>
> I don't much like that free_unused_bufs now has this side effect.
> I think would be better to just add a loop in virtnet_restore.
> Or if you want to keep it there, pls rename the function
> to hint it does more.
It makes sense. I would go for the former. Thanks.
>
>
> >
> > [1]:
> > ------------[ 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@xxxxxxxxxxxxxxx> # v6.11+
> > Signed-off-by: Koichiro Den <koichiro.den@xxxxxxxxxxxxx>
> > ---
> > drivers/net/virtio_net.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 64c87bb48a41..48ce8b3881b6 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -3054,7 +3054,6 @@ 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));
> > 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);
> >
> > @@ -6243,6 +6242,7 @@ static void free_unused_bufs(struct virtnet_info *vi)
> > struct virtqueue *vq = vi->sq[i].vq;
> > while ((buf = virtqueue_detach_unused_buf(vq)) != NULL)
> > virtnet_sq_free_unused_buf(vq, buf);
> > + netdev_tx_reset_queue(netdev_get_tx_queue(vi->dev, i));
> > cond_resched();
> > }
> >
> > --
> > 2.43.0
>
