Re: [PATCH/RFC] remove irqs_disabled warning from local_bh_enable
- From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 17 Jun 2008 16:55:02 -0700 (PDT)
On Tue, 17 Jun 2008, Johannes Berg wrote:
This warning has started to trigger with mac80211 because it can, under
some circumstances, use spin_lock_bh() protected sections within
irq-disabled sections. Is that a bug?
Yes, it's a bug.
Why? Not because of the "spin_lock_bh()" itself, but because of the
_unlock_, which does a "local_bh_enable_ip()", which in turn will check
the whole "do_softirq()" if it was the last softirq_count.
And you must not do softirq's when hard-irq's were disabled!
So it should in theory be ok (but perhaps a bit odd) to do something like
spin_lock_irq(&irq_lock);
..do something..
spin_lock_bh(&bh_lock);
spin_unlock_irq(&irq_lock);
.. do something else ..
spin_unlock_bh(&bh_lock);
where the "spin_lock_bh()" itself is in an irq-locked context - as long as
the "spin_unlock_bh()" is *not*.
See?
Linus
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