linux-kernel - Re: [PATCH v1] Bluetooth: Fix kernel oops triggered by hci_adv_monitors

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Date:   Tue, 30 Jun 2020 14:55:48 -0700
From:   Miao-chen Chou <mcchou@...omium.org>
To:     Marcel Holtmann <marcel@...tmann.org>
Cc:     Bluetooth Kernel Mailing List <linux-bluetooth@...r.kernel.org>,
        Alain Michaud <alainm@...omium.org>,
        Pavel Machek <pavel@....cz>,
        Abhishek Pandit-Subedi <abhishekpandit@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v1] Bluetooth: Fix kernel oops triggered by hci_adv_monitors_clear()

Hi Marcel,

hci_unregister_dev() is invoked when the controller is intended to be
removed by btusb driver. In other words, there should not be any
activity on hdev's workqueue, so the destruction of the workqueue
should be the first thing to do to prevent the clear helpers from
issuing any work. So my suggestion is to revert the patch re-arranging
the workqueue and apply this instead.
I should have uploaded this earlier, but I encountered some troubles
while verifying the changes. Sorry for the inconvenience.

Regards,
Miao

On Mon, Jun 29, 2020 at 11:51 PM Marcel Holtmann <marcel@...tmann.org> wrote:
>
> Hi Miao-chen,
>
> > This fixes the kernel oops by removing unnecessary background scan
> > update from hci_adv_monitors_clear() which shouldn't invoke any work
> > queue.
> >
> > The following test was performed.
> > - Run "rmmod btusb" and verify that no kernel oops is triggered.
> >
> > Signed-off-by: Miao-chen Chou <mcchou@...omium.org>
> > Reviewed-by: Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
> > Reviewed-by: Alain Michaud <alainm@...omium.org>
> > ---
> >
> > net/bluetooth/hci_core.c | 2 --
> > 1 file changed, 2 deletions(-)
> >
> > diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> > index 5577cf9e2c7cd..77615161c7d72 100644
> > --- a/net/bluetooth/hci_core.c
> > +++ b/net/bluetooth/hci_core.c
> > @@ -3005,8 +3005,6 @@ void hci_adv_monitors_clear(struct hci_dev *hdev)
> >               hci_free_adv_monitor(monitor);
> >
> >       idr_destroy(&hdev->adv_monitors_idr);
> > -
> > -     hci_update_background_scan(hdev);
> > }
>
> I am happy to apply this as well, but I also applied another patch re-arranging the workqueue destroy handling. Can you check which prefer or if we should include both patches.
>
> Regards
>
> Marcel
>