netdev - Re: [PATCH] rhashtable: use irq-safe spinlock in rhashtable_rehash

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Date:   Wed, 06 Feb 2019 09:40:12 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     johannes@...solutions.net
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org, j@...fi,
        tgraf@...g.ch, herbert@...dor.apana.org.au
Subject: Re: [PATCH] rhashtable: use irq-safe spinlock in
 rhashtable_rehash_table()

From: Johannes Berg <johannes@...solutions.net>
Date: Wed, 06 Feb 2019 09:15:15 +0100

> On Tue, 2019-02-05 at 15:37 +0100, Johannes Berg wrote:
>> From: Johannes Berg <johannes.berg@...el.com>
>> 
>> When an rhashtabl walk is done from irq/bh context, we rightfully
>> get a lockdep complaint saying that we could get a (soft-)IRQ in
>> the middle of a rehash. This happened e.g. in mac80211 as it does
>> a walk in soft-irq context.
>> 
>> Fix this by using irq-safe locking here. We don't need _irqsave()
>> as we know this will be called only in process context from the
>> workqueue. We could get away with _bh() but that seems a bit less
>> generic, though I'm not sure anyone would want to do a walk from
>> a real IRQ handler.
> 
> Please drop this, it doesn't make sense.
> 
> I'll resend with all the spinlock usage changed to either _bh or
> _irqsave(), since it makes no sense to enforce any kind of outside
> BH/irq disabling for purposes of the inner lock.

Ok.