linux-kernel - Re: [PATCH] staging: rtl8723bs: protect sleepq_len access by sleep

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Date:   Fri, 17 Sep 2021 16:27:42 +0200
From:   Fabio Aiuto <fabioaiuto83@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Hans de Goede <hdegoede@...hat.com>, Larry.Finger@...inger.net,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: rtl8723bs: protect sleepq_len access by
 sleep_q.lock

Hi Greg,

On Fri, Sep 17, 2021 at 04:25:12PM +0200, Greg KH wrote:
> On Mon, Sep 13, 2021 at 05:12:19PM +0200, Hans de Goede wrote:
> > Hi Fabio,
> > 
> > On 9/13/21 3:39 PM, Fabio Aiuto wrote:
> > > Hello Hans,
> > > 
> > > On Mon, Sep 13, 2021 at 03:24:44PM +0200, Hans de Goede wrote:
> > >> Hi Fabio,
> > >>
> > >  
> > >>> Note that sleep_q.lock is already taken inside
> > >>> rtw_free_xmitframe_queue so we just wrap sleepq_len
> > >>> access.
> > >>>
> > >>> Moved pxmitpriv->lock after sleep_q.lock release to
> > >>> avoid locks nesting.
> > > 
> > >>>  	rtw_free_xmitframe_queue(pxmitpriv, &psta->sleep_q);
> > >>> +	spin_lock_bh(&psta->sleep_q.lock);
> > >>
> > >> AFAICT this needs to be above the rtw_free_xmitframe_queue() ?
> > > 
> > > as I wrote on the changelog, the sleep_q.lock is already
> > > taken inside rtw_free_xmitframe_queue. If I put the
> > > sleep_q.lock above that function a soft lock occurs when
> > > I disconnect.
> > > 
> > > So I put it just below rtw_free_xmitframe_queue.
> > > 
> > > Things works fine this way.
> > > 
> > > Please tell me if there's a best way to do it.
> > 
> > Hmm I see, this may work, but the sleepq_len access
> > really should be protected by the same lock as the freeing
> > of the queue is without dropping it in between.
> > 
> > That rtw_free_xmitframe_queue() takes the sleep_q.lock
> > then to me that signals that other (higher-level) functions should
> > not take sleep_q.lock at all, since this is then private to the
> > functions operating on the sleep_q.
> > 
> > I've an idea how we we can possibly tackle this, but I'm not sure
> > yet I will try to make some time to look into this tomorrow or
> > the day after.
> 
> I'm just going to go and revert the original change here until you all
> can sort it out :)

that's the best thing for now ;)

> 
> thanks,
> 
> greg k-h

thank you,

fabio