netdev - Re: [PATCH v2] Bluetooth: When HCI work queue is drained, only queue chained work

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Date:   Fri, 3 Jun 2022 16:12:11 +0800
From:   Schspa Shi <schspa@...il.com>
To:     Luiz Augusto von Dentz <luiz.dentz@...il.com>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        syzbot+63bed493aebbf6872647@...kaller.appspotmail.com
Subject: Re: [PATCH v2] Bluetooth: When HCI work queue is drained, only queue
 chained work

Luiz Augusto von Dentz <luiz.dentz@...il.com> writes:

> Hi Schspa,
>
> On Thu, Jun 2, 2022 at 12:20 PM Schspa Shi <schspa@...il.com> wrote:
>>
>> The HCI command, event, and data packet processing workqueue is drained
>> to avoid deadlock in commit
>> 76727c02c1e1 ("Bluetooth: Call drain_workqueue() before resetting state").
>>
>> There is another delayed work, which will queue command to this drained
>> workqueue. Which results in the following error report:
>>
>> Bluetooth: hci2: command 0x040f tx timeout
>> WARNING: CPU: 1 PID: 18374 at kernel/workqueue.c:1438 __queue_work+0xdad/0x1140
>> Workqueue: events hci_cmd_timeout
>> RIP: 0010:__queue_work+0xdad/0x1140
>> RSP: 0000:ffffc90002cffc60 EFLAGS: 00010093
>> RAX: 0000000000000000 RBX: ffff8880b9d3ec00 RCX: 0000000000000000
>> RDX: ffff888024ba0000 RSI: ffffffff814e048d RDI: ffff8880b9d3ec08
>> RBP: 0000000000000008 R08: 0000000000000000 R09: 00000000b9d39700
>> R10: ffffffff814f73c6 R11: 0000000000000000 R12: ffff88807cce4c60
>> R13: 0000000000000000 R14: ffff8880796d8800 R15: ffff8880796d8800
>> FS:  0000000000000000(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 000000c0174b4000 CR3: 000000007cae9000 CR4: 00000000003506e0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>  <TASK>
>>  ? queue_work_on+0xcb/0x110
>>  ? lockdep_hardirqs_off+0x90/0xd0
>>  queue_work_on+0xee/0x110
>>  process_one_work+0x996/0x1610
>>  ? pwq_dec_nr_in_flight+0x2a0/0x2a0
>>  ? rwlock_bug.part.0+0x90/0x90
>>  ? _raw_spin_lock_irq+0x41/0x50
>>  worker_thread+0x665/0x1080
>>  ? process_one_work+0x1610/0x1610
>>  kthread+0x2e9/0x3a0
>>  ? kthread_complete_and_exit+0x40/0x40
>>  ret_from_fork+0x1f/0x30
>>  </TASK>
>>
>> To fix this, we can add a new HCI_DRAIN_WQ flag, and don't queue the
>> timeout workqueue while command workqueue is draining.
>>
>> Fixes: 76727c02c1e1 ("Bluetooth: Call drain_workqueue() before resetting state")
>> Reported-by: syzbot+63bed493aebbf6872647@...kaller.appspotmail.com
>> Signed-off-by: Schspa Shi <schspa@...il.com>
>>
>> Changelog:
>> v1 -> v2:
>>         - Move the workqueue drain flag to controller flags, and use hci_dev_*_flag.
>>         - Add missing ncmd_timer cancel.
>>         - Clear DRAIN_WORKQUEUE flag after device command flushed.
>> ---
>>  include/net/bluetooth/hci.h |  1 +
>>  net/bluetooth/hci_core.c    | 10 +++++++++-
>>  net/bluetooth/hci_event.c   |  5 +++--
>>  3 files changed, 13 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
>> index fe7935be7dc4..4a45c48eb0d2 100644
>> --- a/include/net/bluetooth/hci.h
>> +++ b/include/net/bluetooth/hci.h
>> @@ -361,6 +361,7 @@ enum {
>>         HCI_QUALITY_REPORT,
>>         HCI_OFFLOAD_CODECS_ENABLED,
>>         HCI_LE_SIMULTANEOUS_ROLES,
>> +       HCI_CMD_DRAIN_WORKQUEUE,
>>
>>         __HCI_NUM_FLAGS,
>>  };
>> diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
>> index 5abb2ca5b129..e908fdc4625c 100644
>> --- a/net/bluetooth/hci_core.c
>> +++ b/net/bluetooth/hci_core.c
>> @@ -593,6 +593,11 @@ static int hci_dev_do_reset(struct hci_dev *hdev)
>>         skb_queue_purge(&hdev->rx_q);
>>         skb_queue_purge(&hdev->cmd_q);
>>
>> +       /* Cancel these not cahined pending work */
>> +       hci_dev_set_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE);
>
> There seems to be a typo on the comment line 'cahined', also perhaps
> you test it before setting it so we don't risk flushing multiple
> times?
>

Yes, it's a typo. Let me upload a v3 patch for this.
The whole set and clear operation are locked by hdev->req_lock. There
is no need to add extra code to test it, it's always cleared at the time.

>> +       cancel_delayed_work(&hdev->cmd_timer);
>> +       cancel_delayed_work(&hdev->ncmd_timer);
>> +
>>         /* Avoid potential lockdep warnings from the *_flush() calls by
>>          * ensuring the workqueue is empty up front.
>>          */
>> @@ -606,6 +611,8 @@ static int hci_dev_do_reset(struct hci_dev *hdev)
>>         if (hdev->flush)
>>                 hdev->flush(hdev);
>>
>> +       hci_dev_clear_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE);
>> +
>>         atomic_set(&hdev->cmd_cnt, 1);
>>         hdev->acl_cnt = 0; hdev->sco_cnt = 0; hdev->le_cnt = 0;
>>
>> @@ -3861,7 +3868,8 @@ static void hci_cmd_work(struct work_struct *work)
>>                         if (res < 0)
>>                                 __hci_cmd_sync_cancel(hdev, -res);
>>
>> -                       if (test_bit(HCI_RESET, &hdev->flags))
>> +                       if (test_bit(HCI_RESET, &hdev->flags) ||
>> +                           hci_dev_test_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE))
>>                                 cancel_delayed_work(&hdev->cmd_timer);
>>                         else
>>                                 schedule_delayed_work(&hdev->cmd_timer,
>> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
>> index af17dfb20e01..7cb956d3abb2 100644
>> --- a/net/bluetooth/hci_event.c
>> +++ b/net/bluetooth/hci_event.c
>> @@ -3768,8 +3768,9 @@ static inline void handle_cmd_cnt_and_timer(struct hci_dev *hdev, u8 ncmd)
>>                         cancel_delayed_work(&hdev->ncmd_timer);
>>                         atomic_set(&hdev->cmd_cnt, 1);
>>                 } else {
>> -                       schedule_delayed_work(&hdev->ncmd_timer,
>> -                                             HCI_NCMD_TIMEOUT);
>> +                       if (!hci_dev_test_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE))
>> +                               schedule_delayed_work(&hdev->ncmd_timer,
>> +                                                     HCI_NCMD_TIMEOUT);
>>                 }
>>         }
>>  }
>> --
>> 2.24.3 (Apple Git-128)
>>

--
BRs

Schspa Shi