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From:   Kalle Valo <kvalo@kernel.org>
To:     <Ajay.Kathat@microchip.com>
Cc:     <linux-wireless@vger.kernel.org>, <Claudiu.Beznea@microchip.com>,
        <Sripad.Balwadgi@microchip.com>, <mwalle@kernel.org>
Subject: Re: [PATCH] wifi: wilc1000: fix kernel oops during interface down during background scan
References: <20230404012010.15261-1-ajay.kathat@microchip.com>
Date:   Fri, 05 May 2023 18:47:07 +0300
In-Reply-To: <20230404012010.15261-1-ajay.kathat@microchip.com> (Ajay Kathat's
        message of "Tue, 4 Apr 2023 01:20:50 +0000")
Message-ID: <87wn1mok5g.fsf@kernel.org>
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<Ajay.Kathat@microchip.com> writes:

> Fix for kernel crash observed with following test procedure [1]:
>   while true;
>     do ifconfig wlan0 up;
>     iw dev wlan0 scan &
>     ifconfig wlan0 down;
>   done
>
> During the above test procedure, the scan results are received from firmware
> for 'iw scan' command gets queued even when the interface is going down. It
> was causing the kernel oops when dereferencing the freed pointers.
>
> For synchronization, 'mac_close()' calls flush_workqueue() to block its
> execution till all pending work is completed. Afterwards 'wilc->close' flag
> which is set before the flush_workqueue() should avoid adding new work.
> Added 'wilc->close' check in wilc_handle_isr() which is common for
> SPI/SDIO bus to ignore the interrupts from firmware that inturns adds the
> work since the interface is getting closed.
>
> 1. https://lore.kernel.org/linux-wireless/20221024135407.7udo3dwl3mqyv2yj@0002.3ffe.de/
>
> Reported-by: Michael Walle <mwalle@kernel.org>
> Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>

[...]

> @@ -781,13 +776,15 @@ static int wilc_mac_close(struct net_device *ndev)
>  	if (vif->ndev) {
>  		netif_stop_queue(vif->ndev);
>
> +		if (wl->open_ifcs == 0)
> +			wl->close = 1;
> +

wl-close is an int, I wonder if it's racy to int as a flag like this? In
cases like this I usually use set_bit() & co because those guarantee
atomicity, though don't know if that's overkill.

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