[PATCH] Bluetooth: When HCI work queue is drained, only queue chained work.

[PATCH] Bluetooth: When HCI work queue is drained, only queue chained work.

[Schspa Shi]

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,
 };
 
 /* 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);
 	/* 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);
 		}
 	}
 }
-- 
2.24.3 (Apple Git-128)

Re: [PATCH] Bluetooth: When HCI work queue is drained, only queue chained work.

[Schspa Shi]

Schspa Shi <schspa@gmail.com> writes:

> 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,
>  };
>
>  /* 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);

Need to add cancel_delayed_work(&hdev->ncmd_timer);
I'll make a new patch after the rest of this patch has been reviewed.

>       /* 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);
>               }
>       }
>  }

---
BRs

Schspa Shi

RE: Bluetooth: When HCI work queue is drained, only queue chained work.

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 1516 bytes --]

This is automated email and please do not reply to this email!

Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/project/bluetooth/list/?series=646337

---Test result---

Test Summary:
CheckPatch                    PASS      2.03 seconds
GitLint                       FAIL      1.10 seconds
SubjectPrefix                 PASS      0.83 seconds
BuildKernel                   PASS      32.53 seconds
BuildKernel32                 PASS      27.94 seconds
Incremental Build with patchesPASS      39.13 seconds
TestRunner: Setup             PASS      481.36 seconds
TestRunner: l2cap-tester      PASS      17.23 seconds
TestRunner: bnep-tester       PASS      6.08 seconds
TestRunner: mgmt-tester       PASS      101.04 seconds
TestRunner: rfcomm-tester     PASS      9.63 seconds
TestRunner: sco-tester        PASS      9.45 seconds
TestRunner: smp-tester        PASS      9.44 seconds
TestRunner: userchan-tester   PASS      6.33 seconds

Details
##############################
Test: GitLint - FAIL - 1.10 seconds
Run gitlint with rule in .gitlint
Bluetooth: When HCI work queue is drained, only queue chained work.
1: T3 Title has trailing punctuation (.): "Bluetooth: When HCI work queue is drained, only queue chained work."
13: B1 Line exceeds max length (85>80): "CPU: 1 PID: 18374 Comm: kworker/1:9 Not tainted 5.18.0-rc6-next-20220516-syzkaller #0"




---
Regards,
Linux Bluetooth

Re: [PATCH] Bluetooth: When HCI work queue is drained, only queue chained work.

[Marcel Holtmann]

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

Re: [PATCH] Bluetooth: When HCI work queue is drained, only queue chained work.

[Schspa Shi]

Marcel Holtmann <marcel@holtmann.org> writes:

> 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?
>

No, it seems this lock can be removed.

I can send a new patch version to remove this.

>>      /* 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

--
BRs

Schspa Shi