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Subject: Re: Linux 5.0 regression: rtl8169 / kernel BUG at
 lib/dynamic_queue_limits.c:27!
To:     Heiner Kallweit <hkallweit1@gmail.com>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Realtek linux nic maintainers <nic_swsd@realtek.com>,
        Eric Dumazet <edumazet@google.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>
References: <6c389fde-4c8d-300b-8c3c-300d6105c30a@eikelenboom.it>
 <0f605e50-56fe-06b5-9b66-6aed89a608ce@gmail.com>
 <471e550b-c227-22e6-19fd-5f9abd450e5f@eikelenboom.it>
 <1265d424-4943-e571-a74b-b1512ebec179@gmail.com>
 <059e59c6-2264-fd5c-068f-3656e39539c1@eikelenboom.it>
 <140d0df7-1775-5457-aa03-b21ece250a72@gmail.com>
 <e6423f51-42cc-e49f-bb48-85ea922f01b6@gmail.com>
 <aa7eb814-ebf7-ffa5-ce61-317b9bbf2394@gmail.com>
 <6b4e8aa0-03c5-c0a8-439e-77daabb07416@eikelenboom.it>
 <70e9a3fe-158a-c3a2-a427-2343bc6c9031@gmail.com>
 <88b80a6b-42e0-ce4e-8aad-4e23a17c7e65@eikelenboom.it>
 <824acd0b-920c-7554-4a63-d80c7de2a8b6@gmail.com>
From:   Sander Eikelenboom <linux@eikelenboom.it>
Message-ID: <302dd169-d981-9d8d-99a6-9d1462e913f9@eikelenboom.it>
Date:   Sun, 10 Feb 2019 10:16:58 +0100
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On 09/02/2019 12:50, Heiner Kallweit wrote:
> On 09.02.2019 11:07, Sander Eikelenboom wrote:
>> On 09/02/2019 10:59, Heiner Kallweit wrote:
>>> On 09.02.2019 10:34, Sander Eikelenboom wrote:
>>>> On 09/02/2019 10:02, Heiner Kallweit wrote:
>>>>> On 09.02.2019 00:09, Eric Dumazet wrote:
>>>>>>
>>>>>>
>>>>>> On 02/08/2019 01:50 PM, Heiner Kallweit wrote:
>>>>>>> On 08.02.2019 22:45, Sander Eikelenboom wrote:
>>>>>>>> On 08/02/2019 22:22, Heiner Kallweit wrote:
>>>>>>>>> On 08.02.2019 21:55, Sander Eikelenboom wrote:
>>>>>>>>>> On 08/02/2019 19:52, Heiner Kallweit wrote:
>>>>>>>>>>> On 08.02.2019 19:29, Sander Eikelenboom wrote:
>>>>>>>>>>>> L.S.,
>>>>>>>>>>>>
>>>>>>>>>>>> While testing a linux 5.0-rc5 kernel (with some patches on top but they don't seem related) under Xen i the nasty splat below, 
>>>>>>>>>>>> that I haven encountered with Linux 4.20.x.
>>>>>>>>>>>>
>>>>>>>>>>>> Unfortunately I haven't got a clear reproducer for this and bisecting could be nasty due to another (networking related) kernel bug.
>>>>>>>>>>>>
>>>>>>>>>>>> If you need more info, want me to run a debug patch etc., please feel free to ask.
>>>>>>>>>>>>
>>>>>>>>>>> Thanks for the report. However I see no change in the r8169 driver between
>>>>>>>>>>> 4.20 and 5.0 with regard to BQL code. Having said that the root cause could
>>>>>>>>>>> be somewhere else. Therefore I'm afraid a bisect will be needed.
>>>>>>>>>>
>>>>>>>>>> Hmm i did some diging and i think:
>>>>>>>>>> bd7153bd83b806bfcc2e79b7a6f43aa653d06ef3 r8169: remove unneeded mmiowb barriers
>>>>>>>>>> 2e6eedb4813e34d8d84ac0eb3afb668966f3f356 r8169: make use of xmit_more and __netdev_sent_queue
>>>>>>>>>> 620344c43edfa020bbadfd81a144ebe5181fc94f net: core: add __netdev_sent_queue as variant of __netdev_tx_sent_queue
>>>>>>>>>>
>>>>>>>>> You're right. Thought this was added in 4.20 already.
>>>>>>>>> The BQL code pattern I copied from the mlx4 driver and so far I haven't heard about
>>>>>>>>> this issue from any user of physical hw. And due to the fact that a lot of mainboards
>>>>>>>>> have onboard Realtek network I have quite a few testers out there.
>>>>>>>>> Does the issue occur under specific circumstances like very high load?
>>>>>>>>
>>>>>>>> Yep, the box is already quite contented with the Xen VM's and if I remember correctly it occurred while kernel compiling
>>>>>>>> on the host.
>>>>>>>>
>>>>>>>>> If indeed the xmit_more patch causes the issue, I think we have to involve Eric Dumazet
>>>>>>>>> as author of the underlying changes.
>>>>>>>>
>>>>>>>> It could also be the barriers weren't that unneeded as assumed.
>>>>>>>
>>>>>>> The barriers were removed after adding xmit_more handling. Therefore it would be good to
>>>>>>> test also with only 
>>>>>>> bd7153bd83b806bfcc2e79b7a6f43aa653d06ef3 r8169: remove unneeded mmiowb barriers
>>>>>>> removed.
>>>>>>>
>>>>>>>> Since we are almost at RC6 i took the liberty to CC Eric now.
>>>>>>>>
>>>>>>> Sure, thanks.
>>>>>>>
>>>>>>>> BTW am i correct these patches are merely optimizations ?
>>>>>>>
>>>>>>> Yes
>>>>>>>
>>>>>>>> If so and concluding they revert cleanly, perhaps it should be considered at this point in the RC's
>>>>>>>> to revert them for 5.0 and try again for 5.1 ?
>>>>>>>>
>>>>>>> Before removing both it would be good to test with only the barrier-removal removed.
>>>>>>>
>>>>>>
>>>>>> Commit 2e6eedb4813e34d8d84ac0eb3afb668966f3f356 r8169: make use of xmit_more and __netdev_sent_queue
>>>>>> looks buggy to me, since the skb might have been freed already on another cpu when you call
>>>>>>
>>>>>> You could try :
>>>>>>
>>>>>> diff --git a/drivers/net/ethernet/realtek/r8169.c b/drivers/net/ethernet/realtek/r8169.c
>>>>>> index 3624e67aef72c92ed6e908e2c99ac2d381210126..f907d484165d9fd775e81bf2bfb9aa4ddedb1c93 100644
>>>>>> --- a/drivers/net/ethernet/realtek/r8169.c
>>>>>> +++ b/drivers/net/ethernet/realtek/r8169.c
>>>>>> @@ -6070,6 +6070,7 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
>>>>>>         dma_addr_t mapping;
>>>>>>         u32 opts[2], len;
>>>>>>         bool stop_queue;
>>>>>> +       bool door_bell;
>>>>>>         int frags;
>>>>>>  
>>>>>>         if (unlikely(!rtl_tx_slots_avail(tp, skb_shinfo(skb)->nr_frags))) {
>>>>>> @@ -6116,6 +6117,8 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
>>>>>>         /* Force memory writes to complete before releasing descriptor */
>>>>>>         dma_wmb();
>>>>>>  
>>>>>> +       door_bell = __netdev_sent_queue(dev, skb->len, skb->xmit_more);
>>>>>> +
>>>>>>         txd->opts1 = rtl8169_get_txd_opts1(opts[0], len, entry);
>>>>>>  
>>>>>>         /* Force all memory writes to complete before notifying device */
>>>>>> @@ -6127,7 +6130,7 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
>>>>>>         if (unlikely(stop_queue))
>>>>>>                 netif_stop_queue(dev);
>>>>>>  
>>>>>> -       if (__netdev_sent_queue(dev, skb->len, skb->xmit_more)) {
>>>>>> +       if (door_bell) {
>>>>>>                 RTL_W8(tp, TxPoll, NPQ);
>>>>>>                 mmiowb();
>>>>>>         }
>>>>>>
>>>>> Thanks a lot for checking and for the proposed fix.
>>>>> Sander, can you try with this patch on top of 5.0-rc5 w/o removing two two commits?
>>>>
>>>> I have done that already during the night .. the results:
>>>> - I can confirm 2e6eedb4813e34d8d84ac0eb3afb668966f3f356 is the first commit which causes hitting the BUG_ON in lib/dynamic_queue_limits.c.
>>>>   (in other word, with only reverting bd7153bd83b806bfcc2e79b7a6f43aa653d06ef3 it still blows up).
>>>>
>>>> - The Eric's patch only applies cleanly with bd7153bd83b806bfcc2e79b7a6f43aa653d06ef3 reverted, so that's what I tested.
>>>>   The patch seems to prevent hitting the BUG_ON in lib/dynamic_queue_limits.c, it has run this night and I gave done a few kernel compiles
>>>>   this morning. How ever during these kernel compiles i'm getting a transmit queue timeout which i haven't seen with 4.20.x, although i regularly
>>>>   compile kernels in the same way as I do now. The only thing I can't say if that is due to this change, or if it's again something else.
>>>>   Which makes me somewhat inclined to go testing the complete revert some more and see if I can trigger the queue timeout on that or not.
>>>>
>>>>   If I can, it is a separate issue.
>>>>   If I can't it seems even with a patch it still seems as a regression in comparison with 4.20.x, for which
>>>>   a revert would be the right thing to do (since as you indicated these are merely optimizations), 
>>>>   which would give us more time for 5.1 to try to solve things on top of the 5.0-release-to-be.
>>>>   (especially since I seem to still have other issues which need to be sorted out and time is limited)
>>>>
>>>>   The timeout in question:
>>>>         [28336.869479] NETDEV WATCHDOG: eth1 (r8169): transmit queue 0 timed out
>>>>         [28336.881498] WARNING: CPU: 0 PID: 6925 at net/sched/sch_generic.c:461 dev_watchdog+0x20b/0x210
>>>>         [28336.893358] Modules linked in:
>>>>         [28336.904106] CPU: 0 PID: 6925 Comm: cc1 Tainted: G      D           5.0.0-rc5-20190208-thp-net-florian-rtl8169-eric-doflr+ #1
>>>>         [28336.917385] Hardware name: MSI MS-7640/890FXA-GD70 (MS-7640)  , BIOS V1.8B1 09/13/2010
>>>>         [28336.928988] RIP: e030:dev_watchdog+0x20b/0x210
>>>>         [28336.940623] Code: 00 49 63 4e e0 eb 90 4c 89 e7 c6 05 ad d8 f1 00 01 e8 a9 32 fd ff 89 d9 48 89 c2 4c 89 e6 48 c7 c7 50 59 89 82 e8 e5 92 4d ff <0f> 0b eb c0 90 48 c7 47 08 00 00 00 00 48 c7 07 00 00 00 00 0f b7
>>>>         [28336.965265] RSP: e02b:ffff88807d403ea0 EFLAGS: 00010286
>>>>         [28336.977465] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff82a69db8
>>>>         [28336.991265] RDX: 0000000000000001 RSI: 0000000000000001 RDI: 0000000000000200
>>>>         [28337.008865] RBP: ffff88807936e41c R08: 0000000000000000 R09: 0000000000000819
>>>>         [28337.022250] R10: 0000000000000202 R11: ffffffff8247ca80 R12: ffff88807936e000
>>>>         [28337.035204] R13: 0000000000000000 R14: ffff88807936e440 R15: 0000000000000001
>>>>         [28337.049832] FS:  00007f53e9bf3840(0000) GS:ffff88807d400000(0000) knlGS:0000000000000000
>>>>         [28337.062524] CS:  e030 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>         [28337.075086] CR2: 00007f53e60c4000 CR3: 000000001a0be000 CR4: 0000000000000660
>>>>         [28337.090052] Call Trace:
>>>>         [28337.103615]  <IRQ>
>>>>         [28337.116587]  ? qdisc_destroy+0x120/0x120
>>>>         [28337.128905]  call_timer_fn+0x19/0x90
>>>>         [28337.141892]  expire_timers+0x8b/0xa0
>>>>         [28337.153354]  run_timer_softirq+0x7e/0x160
>>>>         [28337.165931]  ? handle_irq_event_percpu+0x4c/0x70
>>>>         [28337.176548]  ? handle_percpu_irq+0x32/0x50
>>>>         [28337.186734]  __do_softirq+0xed/0x229
>>>>         [28337.196404]  ? hypervisor_callback+0xa/0x20
>>>>         [28337.207822]  irq_exit+0xb7/0xc0
>>>>         [28337.218978]  xen_evtchn_do_upcall+0x27/0x40
>>>>         [28337.230763]  xen_do_hypervisor_callback+0x29/0x40
>>>>         [28337.241261]  </IRQ>
>>>>         [28337.253283] RIP: e033:0xff7e62
>>>>         [28337.264899] Code: 35 43 0f c7 00 4c 89 ef e8 8b 6d 67 ff 0f 1f 00 44 89 e0 44 89 e2 c1 e8 06 83 e2 3f 48 8b 0c c5 40 8d c6 01 48 0f a3 d1 72 0e <48> 8b 04 c5 50 8d c6 01 48 0f a3 d0 73 0b 44 89 e6 4c 89 ef e8 b5
>>>>         [28337.288677] RSP: e02b:00007fff0fc6a340 EFLAGS: 00000202
>>>>         [28337.299234] RAX: 0000000000000000 RBX: 00007f53e60c3580 RCX: 0000000000000000
>>>>         [28337.309577] RDX: 0000000000000034 RSI: 0000000001e71a98 RDI: 00007fff0fc6a538
>>>>         [28337.320724] RBP: 00007fff0fc6a4b0 R08: 0000000000000000 R09: 0000000000000000
>>>>         [28337.331829] R10: 0000000000000001 R11: 00000000020cb3d0 R12: 0000000000000034
>>>>         [28337.343900] R13: 00007fff0fc6a538 R14: 0000000000000000 R15: 0000000000000001
>>>>         [28337.353977] ---[ end trace 6ff49f09286816b7 ]---
>>>>
>>> Thanks for your efforts. As usual this tx timeout trace says basically nothing except
>>> "timeout" and root cause could be anything. Earlier you reported a memory allocation error,
>>> did that occur again?
>>> If we decide to revert, I'd leave removal of the memory barriers in (as it doesn't seem to
>>> contribute to the issue) and just submit a patch to effectively revert
>>> 2e6eedb4813e34d8d84ac0eb3afb668966f3f356.
>>
>> I can't say if that is correct, because i haven't tested that.
>>
>> Another thing I could test is:
>>  - putting all the r8169 patches (and prerequisites) that went into 5.0 
>>    up to bd7153bd83b806bfcc2e79b7a6f43aa653d06ef3, onto 4.20.7 and see what that does.
>>    If that would be feasible (not too many needed prerequisites out of r8169) and if 
>>    you could spare me some time and prep such a branch somewhere so i can pull and compile that,
>>    that would be great.
>>
> 
> Unfortunately there's quite a number of changes. Regarding __netdev_tx_sent_queue()
> and watchdog timeout I found the following comment in drivers/net/ethernet/sfc/tx.c,
> efx_enqueue_skb():
> 
> 	if (__netdev_tx_sent_queue(tx_queue->core_txq, skb_len, xmit_more)) {
> 		struct efx_tx_queue *txq2 = efx_tx_queue_partner(tx_queue);
> 
> 		/* There could be packets left on the partner queue if those
> 		 * SKBs had skb->xmit_more set. If we do not push those they
> 		 * could be left for a long time and cause a netdev watchdog.
> 		 */
> 		if (txq2->xmit_more_available)
> 			efx_nic_push_buffers(txq2);
> 
> But I'm not sure whether the situation in r8169 is comparable. The following patch
> implements what I mentioned earlier: It leaves all other 5.0 changes in place and
> effectively reverts 2e6eedb4813e34d8d84ac0eb3afb668966f3f356. Would be great if
> you could give it a try.

Hi Heiner,

It took some time to respond, because I had another issue with 5.0 which intervened with proper testing, 
but fortunately I could pinpoint without doing a full bisect and revert that commit for further testing.

So there is still time left and I could do a more proper run with your patch below.
Unfortunately i still get a splat (see below) with this, although i'm not sure it is related, 
just that I can't tell.

Perhaps Linus as Oops-decoding-guru has an idea ?

--
Sander

[39041.689007] dpkg-deb: page allocation failure: order:0, mode:0x480020(GFP_ATOMIC), nodemask=(null),cpuset=/,mems_allowed=0
[39041.689016] CPU: 4 PID: 14078 Comm: dpkg-deb Not tainted 5.0.0-rc5-20190209-kallweit+ #1
[39041.689017] Hardware name: MSI MS-7640/890FXA-GD70 (MS-7640)  , BIOS V1.8B1 09/13/2010
[39041.689018] Call Trace:
[39041.689022]  <IRQ>
[39041.689030]  dump_stack+0x5c/0x7b
[39041.689033]  warn_alloc+0x103/0x190
[39041.689036]  __alloc_pages_nodemask+0xe3d/0xe80
[39041.689039]  ? ip_rcv+0x48/0xc0
[39041.689040]  ? ip_rcv_finish_core.isra.0+0x360/0x360
[39041.689042]  page_frag_alloc+0x117/0x150
[39041.689044]  __napi_alloc_skb+0x83/0xd0
[39041.689048]  rtl8169_poll+0x210/0x640
[39041.689051]  net_rx_action+0x23d/0x370
[39041.689054]  __do_softirq+0xed/0x229
[39041.689058]  irq_exit+0xb7/0xc0
[39041.689061]  xen_evtchn_do_upcall+0x27/0x40
[39041.689063]  xen_do_hypervisor_callback+0x29/0x40
[39041.689064]  </IRQ>
[39041.689066] RIP: e030:_atomic_dec_and_lock+0x2/0x40
[39041.689068] Code: ff 39 05 c5 c1 c9 00 89 c7 89 c6 76 0f 83 eb 01 83 fb ff 75 d9 5b 89 f8 5d 41 5c c3 0f 0b 90 90 90 90 90 90 90 90 90 90 8b 07 <83> f8 01 74 0c 8d 50 ff f0 0f b1 17 75 f2 31 c0 c3 55 53 48 89 fb
[39041.689069] RSP: e02b:ffffc9000705b990 EFLAGS: 00000246
[39041.689071] RAX: 0000000000000001 RBX: ffff888017082640 RCX: 0000000000000000
[39041.689071] RDX: 0000000000000000 RSI: ffff8880170826c0 RDI: ffff888017082788
[39041.689072] RBP: ffff8880170826c0 R08: ffffc9000705bb00 R09: ffffc9000705bb00
[39041.689073] R10: ffffc9000705bb58 R11: ffff88807fc17000 R12: ffff888017082788
[39041.689073] R13: ffff88806cc8cf58 R14: ffff888017082640 R15: ffff888009990240
[39041.689077]  iput+0x63/0x1a0
[39041.689079]  __dentry_kill+0xc5/0x170
[39041.689080]  shrink_dentry_list+0x93/0x1c0
[39041.689082]  prune_dcache_sb+0x4d/0x70
[39041.689084]  super_cache_scan+0x104/0x190
[39041.689087]  do_shrink_slab+0x12c/0x1e0
[39041.689089]  shrink_slab+0xdf/0x2b0
[39041.689091]  shrink_node+0x158/0x470
[39041.689093]  do_try_to_free_pages+0xd1/0x380
[39041.689095]  try_to_free_pages+0xb2/0xe0
[39041.689097]  __alloc_pages_nodemask+0x603/0xe80
[39041.689099]  ? __pagevec_lru_add_fn+0x1b1/0x290
[39041.689102]  alloc_pages_vma+0x7b/0x1c0
[39041.689106]  __handle_mm_fault+0xdb3/0x1060
[39041.689109]  ? xen_mc_flush+0xc0/0x190
[39041.689110]  handle_mm_fault+0xf8/0x200
[39041.689113]  __do_page_fault+0x231/0x4a0
[39041.689115]  ? page_fault+0x8/0x30
[39041.689116]  page_fault+0x1e/0x30
[39041.689118] RIP: e033:0x7fb9851d012e
[39041.689119] Code: 29 c2 48 3b 15 7b a3 31 00 0f 87 af 00 00 00 0f 10 01 0f 10 49 f0 0f 10 51 e0 0f 10 59 d0 48 83 e9 40 48 83 ea 40 41 0f 29 01 <41> 0f 29 49 f0 41 0f 29 51 e0 41 0f 29 59 d0 49 83 e9 40 48 83 fa
[39041.689119] RSP: e02b:00007fb958b36d38 EFLAGS: 00010202
[39041.689120] RAX: 00007fb97a617f0e RBX: 000000000000f004 RCX: 00007fb948008be3
[39041.689121] RDX: 00000000000080c2 RSI: 00007fb948000b31 RDI: 00007fb97a617f0e
[39041.689122] RBP: 00000000000ff062 R08: 0000000000000002 R09: 00007fb97a620000
[39041.689123] R10: 0000000000000004 R11: 00007fb97a626f02 R12: 000000000000f005
[39041.689123] R13: 00007fb948000b28 R14: 0000562d76b63710 R15: 0000000000000003
[39041.689125] Mem-Info:
[39041.689130] active_anon:78775 inactive_anon:49211 isolated_anon:0
                active_file:106409 inactive_file:107531 isolated_file:0
                unevictable:552 dirty:175 writeback:0 unstable:0
                slab_reclaimable:13739 slab_unreclaimable:16454
                mapped:1605 shmem:23 pagetables:2900 bounce:0
                free:3681 free_pcp:935 free_cma:0
[39041.689132] Node 0 active_anon:315100kB inactive_anon:196844kB active_file:425636kB inactive_file:430124kB unevictable:2208kB isolated(anon):0kB isolated(file):0kB mapped:6420kB dirty:700kB writeback:0kB shmem:92kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 0kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no
[39041.689133] Node 0 DMA free:7480kB min:44kB low:56kB high:68kB active_anon:0kB inactive_anon:7832kB active_file:472kB inactive_file:4kB unevictable:0kB writepending:0kB present:15956kB managed:15872kB mlocked:0kB kernel_stack:0kB pagetables:12kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
[39041.689136] lowmem_reserve[]: 0 1865 1865 1865
[39041.689138] Node 0 DMA32 free:7244kB min:19472kB low:21380kB high:23288kB active_anon:315360kB inactive_anon:188144kB active_file:425164kB inactive_file:430120kB unevictable:2208kB writepending:700kB present:2080768kB managed:1674968kB mlocked:2208kB kernel_stack:9632kB pagetables:11588kB bounce:0kB free_pcp:3740kB local_pcp:528kB free_cma:0kB
[39041.689140] lowmem_reserve[]: 0 0 0 0
[39041.689142] Node 0 DMA: 6*4kB (UME) 6*8kB (UE) 7*16kB (UME) 6*32kB (ME) 5*64kB (UME) 3*128kB (UE) 5*256kB (UME) 2*512kB (ME) 2*1024kB (UE) 1*2048kB (M) 0*4096kB = 7480kB
[39041.689148] Node 0 DMA32: 69*4kB (U) 315*8kB (UE) 138*16kB (UE) 70*32kB (UE) 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 7244kB
[39041.689153] 214701 total pagecache pages
[39041.689155] 273 pages in swap cache
[39041.689156] Swap cache stats: add 100978, delete 100706, find 1158/1257
[39041.689156] Free swap  = 3790588kB
[39041.689157] Total swap = 4194300kB
[39041.689157] 524181 pages RAM
[39041.689158] 0 pages HighMem/MovableOnly
[39041.689158] 101471 pages reserved
[39041.689159] 0 pages cma reserved


> diff --git a/drivers/net/ethernet/realtek/r8169.c b/drivers/net/ethernet/realtek/r8169.c
> index e8a112149..3cca2ffb2 100644
> --- a/drivers/net/ethernet/realtek/r8169.c
> +++ b/drivers/net/ethernet/realtek/r8169.c
> @@ -6192,7 +6192,6 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
>  	struct device *d = tp_to_dev(tp);
>  	dma_addr_t mapping;
>  	u32 opts[2], len;
> -	bool stop_queue;
>  	int frags;
>  
>  	if (unlikely(!rtl_tx_slots_avail(tp, skb_shinfo(skb)->nr_frags))) {
> @@ -6234,6 +6233,8 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
>  
>  	txd->opts2 = cpu_to_le32(opts[1]);
>  
> +	netdev_sent_queue(dev, skb->len);
> +
>  	skb_tx_timestamp(skb);
>  
>  	/* Force memory writes to complete before releasing descriptor */
> @@ -6246,14 +6247,14 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
>  
>  	tp->cur_tx += frags + 1;
>  
> -	stop_queue = !rtl_tx_slots_avail(tp, MAX_SKB_FRAGS);
> -	if (unlikely(stop_queue))
> -		netif_stop_queue(dev);
> -
> -	if (__netdev_sent_queue(dev, skb->len, skb->xmit_more))
> -		RTL_W8(tp, TxPoll, NPQ);
> +	RTL_W8(tp, TxPoll, NPQ);
>  
> -	if (unlikely(stop_queue)) {
> +	if (!rtl_tx_slots_avail(tp, MAX_SKB_FRAGS)) {
> +		/* Avoid wrongly optimistic queue wake-up: rtl_tx thread must
> +		 * not miss a ring update when it notices a stopped queue.
> +		 */
> +		smp_wmb();
> +		netif_stop_queue(dev);
>  		/* Sync with rtl_tx:
>  		 * - publish queue status and cur_tx ring index (write barrier)
>  		 * - refresh dirty_tx ring index (read barrier).
>