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Date:   Sun, 3 Apr 2022 00:13:55 +0300
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Subject: Re: staging: r8188eu: how to handle nested mutex under spinlock
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To:     Michael Straube <straube.linux@gmail.com>
Cc:     Larry Finger <Larry.Finger@lwfinger.net>,
        Phillip Potter <phil@philpotter.co.uk>,
        "open list:STAGING SUBSYSTEM" <linux-staging@lists.linux.dev>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Greg KH <gregkh@linuxfoundation.org>
References: <356c24cf-625b-eea2-2c04-ce132d881cac@gmail.com>
From:   Pavel Skripkin <paskripkin@gmail.com>
In-Reply-To: <356c24cf-625b-eea2-2c04-ce132d881cac@gmail.com>
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Hi Michael,

On 4/2/22 23:47, Michael Straube wrote:
> Hi all,
> 
> smatch reported a sleeping in atomic context.
> 
> rtw_set_802_11_disassociate() <- disables preempt
> -> _rtw_pwr_wakeup()
>      -> ips_leave()
> 
> rtw_set_802_11_disassociate() takes a spinlock and ips_leave() uses a
> mutex.
> 
> I'm fairly new to the locking stuff, but as far as I know this is not a
> false positive since mutex can sleep, but that's not allowed under a
> spinlock.
> 
> What is the best way to handle this?
> I'm not sure if converting the mutex to a spinlock (including all the
> other places where the mutex is used) is the right thing to do?
> 

I've looked into this like a month ago.

IMO, this code just need to be redesigned, since locking scheme is very 
complicated there and, as smatch says, not correct.

Simple s/mutex_lock/spin_lock/ may work in that case, but one day 
locking scheme should be reworked... Or just some code parts should be 
dropped :))


With regards,
Pavel Skripkin