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Date:   Tue, 18 May 2021 19:16:24 -0400
From:   Tong Zhu <zhutong@amazon.com>
To:     <linux-wireless@vger.kernel.org>, <kvalo@qca.qualcomm.com>,
        <toke@toke.dk>, <nbd@nbd.name>
CC:     <zhutong@amazon.com>
Subject: ath9k: possible bug with AR93xx during background scanning
Message-ID: <20210518231612.GA29178@ucf43ac461c9a53.ant.amazon.com>
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Hello

After moving to kernel 4.14 from 4.1, our station with an AR93xx pcie card began
to see packet loss during background scanning. After inspecting the changes, I
realized ath9k no longer pushes to stop traffic at VIF for off-channel scan after
this change.

50f08edf98096a68f01ff4566b605a25bf8e42ce ath9k: Switch to using mac80211 intermediate software queues.

Here is a snippet of a ftrace function sequence during a scan.

    kworker/u4:0-28892 [001] .n.....  3082.957750: ieee80211_offchannel_stop_vifs <-ieee80211_scan_work
  XX-XXXXXXXXXXd-489   [001] .....12  3082.971105: __ieee80211_subif_start_xmit <-ieee80211_subif_start_xmit
  XX-XXXXXXXXXXd-489   [001] .....14  3082.971128: ath_tx_txqaddbuf <-ath_txq_schedule
   irq/175-ath9k-189   [001] .....15  3082.998888: ath_tx_process_buffer <-ath_tx_edma_tasklet
   irq/175-ath9k-189   [001] .....16  3082.998898: ath_tx_txqaddbuf <-ath_txq_schedule
   irq/175-ath9k-189   [000] .....15  3083.011497: ath_tx_process_buffer <-ath_tx_edma_tasklet
   irq/175-ath9k-189   [000] .....16  3083.011504: ath_tx_txqaddbuf <-ath_txq_schedule
   irq/175-ath9k-189   [001] .....15  3083.022261: ath_tx_process_buffer <-ath_tx_edma_tasklet
   irq/175-ath9k-189   [001] .....16  3083.022268: ath_tx_txqaddbuf <-ath_txq_schedule
   irq/175-ath9k-189   [000] .....15  3083.034131: ath_tx_process_buffer <-ath_tx_edma_tasklet
   irq/175-ath9k-189   [000] .....15  3083.034134: ath_tx_complete_buf <-ath_tx_process_buffer
   irq/175-ath9k-189   [000] .....15  3083.034136: ath_tx_complete <-ath_tx_complete_buf
    kworker/u4:0-28892 [001] .......  3083.083246: ieee80211_offchannel_return <-ieee80211_scan_work

Between timestamp 3082.957750 and 3083.083246, the device went off channel. A packet
came down and reached hardware queue. Hardware TX processing continued. It is a
serious issue if PDUs are indeed sent out during off-channel.

Regards,
Tong