Message-ID: <75967109-85e4-46ce-9952-94dcb98f5513@redhat.com>
Date: Tue, 10 Dec 2024 11:20:08 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Koichiro Den <koichiro.den@...onical.com>, virtualization@...ts.linux.dev
Cc: mst@...hat.com, jasowang@...hat.com, xuanzhuo@...ux.alibaba.com,
 eperezma@...hat.com, andrew+netdev@...n.ch, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, jiri@...nulli.us,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH net v4 1/6] virtio_net: correct netdev_tx_reset_queue()
 invocation point

On 12/6/24 02:10, 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]. 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. As a result, netdev_tx_reset_queue() is now
> explicitly required in freeze/restore path. This patch adds it to
> immediately after free_unused_bufs(), following the rule of thumb:
> netdev_tx_reset_queue() should follow any SKB freeing not followed by
> netdev_tx_completed_queue(). This seems the most consistent and
> streamlined approach, and now netdev_tx_reset_queue() runs whenever
> free_unused_bufs() is done.
> 
> [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 ]---

IIRC, the above separator used to cause some troubles to backport tools
and to 'next' tree import, trimming the SoB area below. I'm going to
remove it while applying the series.

Cheers,

Paolo

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