Message-ID: <20241205052729-mutt-send-email-mst@kernel.org>
Date: Thu, 5 Dec 2024 05:33:36 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Koichiro Den <koichiro.den@...onical.com>
Cc: virtualization@...ts.linux.dev, jasowang@...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, jiri@...nulli.us,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH net-next v3 1/7] virtio_net: correct
 netdev_tx_reset_queue() invocation point

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?

> 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.


> 
> [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@...r.kernel.org> # v6.11+
> Signed-off-by: Koichiro Den <koichiro.den@...onical.com>
> ---
>  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

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