linux-kernel - Re: [PATCH] bluetooth: remove WQ_MEM

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Message-Id: <7BDF7BD6-EF2C-414D-B5A3-331374180282@holtmann.org>
Date:   Thu, 29 Jun 2017 14:37:21 +0200
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Dominik Brodowski <linux@...inikbrodowski.net>,
        "Gustavo F. Padovan" <gustavo@...ovan.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-bluetooth@...r.kernel.org
Subject: Re: [PATCH] bluetooth: remove WQ_MEM_RECLAIM from hci workqueues

Hi Tejun,

> Bluetooth hci uses ordered HIGHPRI, MEM_RECLAIM workqueues.  It's
> likely that the flags came from mechanical conversion from
> create_singlethread_workqueue().  Bluetooth shouldn't be depended upon
> for memory reclaim and the spurious MEM_RECLAIM flag can trigger the
> following warning.  Remove WQ_MEM_RECLAIM and convert to
> alloc_ordered_workqueue() while at it.
> 
>  workqueue: WQ_MEM_RECLAIM hci0:hci_power_off is flushing !WQ_MEM_RECLAIM events:btusb_work
>  ------------[ cut here ]------------
>  WARNING: CPU: 2 PID: 14231 at /home/brodo/local/kernel/git/linux/kernel/workqueue.c:2423 check_flush_dependency+0xb3/0x100
>  Modules linked in:
>  CPU: 2 PID: 14231 Comm: kworker/u9:4 Not tainted 4.12.0-rc6+ #3
>  Hardware name: Dell Inc. XPS 13 9343/0TM99H, BIOS A11 12/08/2016
>  Workqueue: hci0 hci_power_off
>  task: ffff9432dad58000 task.stack: ffff986d43790000
>  RIP: 0010:check_flush_dependency+0xb3/0x100
>  RSP: 0018:ffff986d43793c90 EFLAGS: 00010086
>  RAX: 000000000000005a RBX: ffff943316810820 RCX: 0000000000000000
>  RDX: 0000000000000000 RSI: 0000000000000096 RDI: 0000000000000001
>  RBP: ffff986d43793cb0 R08: 0000000000000775 R09: ffffffff85bdd5c0
>  R10: 0000000000000040 R11: 0000000000000000 R12: ffffffff84d596e0
>  R13: ffff9432dad58000 R14: ffff94321c640320 R15: ffff9432dad58000
>  FS:  0000000000000000(0000) GS:ffff94331f500000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 00007b8bca242000 CR3: 000000014f60a000 CR4: 00000000003406e0
>  Call Trace:
>   flush_work+0x8a/0x1c0
>   ? flush_work+0x184/0x1c0
>   ? skb_free_head+0x21/0x30
>   __cancel_work_timer+0x124/0x1b0
>   ? hci_dev_do_close+0x2a4/0x4d0
>   cancel_work_sync+0x10/0x20
>   btusb_close+0x23/0x100
>   hci_dev_do_close+0x2ca/0x4d0
>   hci_power_off+0x1e/0x50
>   process_one_work+0x184/0x3e0
>   worker_thread+0x4a/0x3a0
>   ? preempt_count_sub+0x9b/0x100
>   ? preempt_count_sub+0x9b/0x100
>   kthread+0x125/0x140
>   ? process_one_work+0x3e0/0x3e0
>   ? __kthread_create_on_node+0x1a0/0x1a0
>   ? do_syscall_64+0x58/0xd0
>   ret_from_fork+0x27/0x40
>  Code: 00 75 bf 49 8b 56 18 48 8d 8b b0 00 00 00 48 81 c6 b0 00 00 00 4d 89 e0 48 c7 c7 20 23 6b 85 c6 05 83 cd 31 01 01 e8 bf c4 0c 00 <0f> ff eb 93 80 3d 74 cd 31 01 00 75 a5 65 48 8b 04 25 00 c5 00 
>  ---[ end trace b88fd2f77754bfec ]---
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Dominik Brodowski <linux@...inikbrodowski.net>
> ---
> Hello,
> 
> Marcel, as this isn't urgent and there is slight chance that this
> might trigger another warning if these work items get flushed from a
> different MEM_RECLAIM work item from e.g. nfs over network over
> bluetooth.  Can you please try applying the patch after the 4.13-rc1
> closes and see whether it turns up anything else?
> 
> Thanks.
> 
> net/bluetooth/hci_core.c |    7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)

patch has been applied to bluetooth-next tree.

Regards

Marcel