linux-kernel - Re: [PATCH] b43legacy: Fix a sleep-in-atomic bug in b43legacy_attr_interfmode

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Message-ID: <20170531171715.58d6c084@wiggum>
Date:   Wed, 31 May 2017 17:17:15 +0200
From:   Michael Büsch <m@...s.ch>
To:     Jia-Ju Bai <baijiaju1990@....com>
Cc:     Larry.Finger@...inger.net, kvalo@...eaurora.org,
        netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
        b43-dev@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] b43legacy: Fix a sleep-in-atomic bug in
 b43legacy_attr_interfmode_store

On Wed, 31 May 2017 18:29:07 +0800
Jia-Ju Bai <baijiaju1990@....com> wrote:

> The driver may sleep under a spin lock, and the function call path is:
> b43legacy_attr_interfmode_store (acquire the lock by spin_lock_irqsave)
>   b43legacy_radio_set_interference_mitigation
>     b43legacy_radio_interference_mitigation_disable
>       b43legacy_calc_nrssi_slope
>         b43legacy_synth_pu_workaround
>           might_sleep and msleep --> may sleep
> 
> Fixing it may be complex, and a possible way is to remove 
> spin_lock_irqsave and spin_lock_irqrestore in 
> b43legacy_attr_interfmode_store, and the code has been protected by
> mutex_lock and mutex_unlock.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@....com>
> ---
>  drivers/net/wireless/broadcom/b43legacy/sysfs.c |    2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/broadcom/b43legacy/sysfs.c b/drivers/net/wireless/broadcom/b43legacy/sysfs.c
> index 2a1da15..9ede143 100644
> --- a/drivers/net/wireless/broadcom/b43legacy/sysfs.c
> +++ b/drivers/net/wireless/broadcom/b43legacy/sysfs.c
> @@ -137,14 +137,12 @@ static ssize_t b43legacy_attr_interfmode_store(struct device *dev,
>  	}
>  
>  	mutex_lock(&wldev->wl->mutex);
> -	spin_lock_irqsave(&wldev->wl->irq_lock, flags);
>  
>  	err = b43legacy_radio_set_interference_mitigation(wldev, mode);
>  	if (err)
>  		b43legacyerr(wldev->wl, "Interference Mitigation not "
>  		       "supported by device\n");
>  	mmiowb();
> -	spin_unlock_irqrestore(&wldev->wl->irq_lock, flags);
>  	mutex_unlock(&wldev->wl->mutex);
>  
>  	return err ? err : count;


Interference mitigation has never been properly implemented and tested.
As such nobody should use it and I would be surprised if anybody uses
this attribute.
So I would suggest to remove this sysfs attribute entirely instead of
having this incorrect fix.

-- 
Michael

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