linux-kernel - Re: [PATCH] Bluetooth: hci_qca: Use del_timer

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Date:   Wed, 6 Apr 2022 08:39:07 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        Ben Young Tae Kim <ytkim@....qualcomm.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] Bluetooth: hci_qca: Use del_timer_sync() before freeing

On Mon, Apr 04, 2022 at 05:22:00PM -0700, Eric Dumazet wrote:
> 
> On 4/4/22 15:22, Steven Rostedt wrote:
> > [ Resending due to cut and paste failure of email address ]
> > 
> > From: Steven Rostedt (Google) <rostedt@...dmis.org>
> > 
> > While looking at a crash report on a timer list being corrupted, which
> > usually happens when a timer is freed while still active. This is
> > commonly triggered by code calling del_timer() instead of
> > del_timer_sync() just before freeing.
> > 
> > One possible culprit is the hci_qca driver, which does exactly that.
> > 
> > Cc: stable@...r.kernel.org
> > Fixes: 0ff252c1976da ("Bluetooth: hciuart: Add support QCA chipset for
> > UART") Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> > ---
> > diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
> > index f6e91fb432a3..73a8c72b5aae 100644
> > --- a/drivers/bluetooth/hci_qca.c
> > +++ b/drivers/bluetooth/hci_qca.c
> > @@ -696,8 +696,8 @@ static int qca_close(struct hci_uart *hu)
> >   	skb_queue_purge(&qca->tx_wait_q);
> >   	skb_queue_purge(&qca->txq);
> >   	skb_queue_purge(&qca->rx_memdump_q);
> > -	del_timer(&qca->tx_idle_timer);
> > -	del_timer(&qca->wake_retrans_timer);
> > +	del_timer_sync(&qca->tx_idle_timer);
> > +	del_timer_sync(&qca->wake_retrans_timer);
> 
> 
> It seems the wake_retrans_timer could be re-armed from a work queue.
> 
> So perhaps we need to make sure qca->workqueue is destroyed
> 
> before these del_timer_sync() calls ?
> 
> >   	destroy_workqueue(qca->workqueue);
> 
> 
> ie move this destroy_workqueue() up ?
> 

What prevents the timer code from queueing work into the destroyed
workqueue ?

Thanks,
Guenter