linux-kernel - Re: BUG: soft lockup in ieee80211_tasklet

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Message-ID: <0a0573f07a7e1468f83d52afcf8f5ba356725740.camel@sipsolutions.net>
Date:   Tue, 02 Mar 2021 15:18:16 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Hillf Danton <hdanton@...a.com>,
        syzbot <syzbot+27df43cf7ae73de7d8ee@...kaller.appspotmail.com>
Cc:     linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: BUG: soft lockup in ieee80211_tasklet_handler

On Wed, 2021-02-24 at 10:30 +0800, Hillf Danton wrote:
> 
> Add budget for the 80211 softint handler - it's feasible not to try to
> build the giant pyramid in a week.
> 
> --- x/net/mac80211/main.c
> +++ y/net/mac80211/main.c
> @@ -224,9 +224,15 @@ static void ieee80211_tasklet_handler(un
>  {
>  	struct ieee80211_local *local = (struct ieee80211_local *) data;
>  	struct sk_buff *skb;
> +	int i = 0;
> +
> +	while (i++ < 64) {
> +		skb = skb_dequeue(&local->skb_queue);
> +		if (!skb)
> +			skb = skb_dequeue(&local->skb_queue_unreliable);
> +		if (!skb)
> +			return;

I guess that's not such a bad idea, but I do wonder how we get here,
userspace can submit packets faster than we can process?

It feels like a simulation-only case, tbh, since over the air you have
limits how much bandwidth you can get ... unless you have a very slow
CPU?

In any case, if you want anything merged you're going to have to submit
a proper patch with a real commit message and Signed-off-by, etc.

johannes