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Subject: Re: [PATCH] Bluetooth: When HCI work queue is drained, only queue
 chained work.
From:   Marcel Holtmann <marcel@holtmann.org>
In-Reply-To: <20220531184124.20577-1-schspa@gmail.com>
Date:   Thu, 2 Jun 2022 17:37:51 +0200
Cc:     Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
        "David S. Miller" <davem@davemloft.net>, edumazet@google.com,
        kuba@kernel.org, pabeni@redhat.com,
        linux-bluetooth@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        syzbot+63bed493aebbf6872647@syzkaller.appspotmail.com
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References: <20220531184124.20577-1-schspa@gmail.com>
To:     Schspa Shi <schspa@gmail.com>
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Hi Schspa,

> 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
> Modules linked in:
> CPU: 1 PID: 18374 Comm: kworker/1:9 Not tainted 5.18.0-rc6-next-20220516-syzkaller #0
> 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@syzkaller.appspotmail.com
> Signed-off-by: Schspa Shi <schspa@gmail.com>
> ---
> include/net/bluetooth/hci.h | 1 +
> net/bluetooth/hci_core.c    | 8 +++++++-
> net/bluetooth/hci_event.c   | 5 +++--
> 3 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
> index fe7935be7dc4..c2cba0a621d3 100644
> --- a/include/net/bluetooth/hci.h
> +++ b/include/net/bluetooth/hci.h
> @@ -291,6 +291,7 @@ enum {
> 	HCI_RAW,
> 
> 	HCI_RESET,
> +	HCI_DRAIN_WQ,
> };

no addition to this enum please. This is ABI. Use the other one and hci_dev_{set,clear}_flag.

> 
> /* HCI socket flags */
> diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> index 5abb2ca5b129..ef3bd543ce04 100644
> --- a/net/bluetooth/hci_core.c
> +++ b/net/bluetooth/hci_core.c
> @@ -593,6 +593,10 @@ static int hci_dev_do_reset(struct hci_dev *hdev)
> 	skb_queue_purge(&hdev->rx_q);
> 	skb_queue_purge(&hdev->cmd_q);
> 
> +	hci_dev_lock(hdev);
> +	set_bit(HCI_DRAIN_WQ, &hdev->flags);
> +	hci_dev_unlock(hdev);
> +	cancel_delayed_work(&hdev->cmd_timer);

Do you need to the locking here?

> 	/* Avoid potential lockdep warnings from the *_flush() calls by
> 	 * ensuring the workqueue is empty up front.
> 	 */
> @@ -601,6 +605,7 @@ static int hci_dev_do_reset(struct hci_dev *hdev)
> 	hci_dev_lock(hdev);
> 	hci_inquiry_cache_flush(hdev);
> 	hci_conn_hash_flush(hdev);
> +	clear_bit(HCI_DRAIN_WQ, &hdev->flags);
> 	hci_dev_unlock(hdev);
> 
> 	if (hdev->flush)
> @@ -3861,7 +3866,8 @@ 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) ||
> +			    test_bit(HCI_DRAIN_WQ, &hdev->flags))
> 				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..700cd01df3a1 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 (!test_bit(HCI_DRAIN_WQ, &hdev->flags))
> +				schedule_delayed_work(&hdev->ncmd_timer,
> +						      HCI_NCMD_TIMEOUT);
> 		}
> 	}
> }

Regards

Marcel