Re: [PATCH/RFC] remove irqs_disabled warning from local_bh_enable
- From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- Date: Wed, 18 Jun 2008 09:01:54 +0200
On Tue, 2008-06-17 at 16:55 -0700, Linus Torvalds wrote:
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*.
I would suggest discouraging such madne^Wcreativity, its gains are
dubious at best and it doesn't make the locking any more obvious and
could be an indication of messy locking to begin with.
So I would like to see Johannes' other patch that allows all of us to
enjoy the warning he ran into ;-)
Peter
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- References:
- [PATCH/RFC] remove irqs_disabled warning from local_bh_enable
- From: Johannes Berg
- Re: [PATCH/RFC] remove irqs_disabled warning from local_bh_enable
- From: Linus Torvalds
- [PATCH/RFC] remove irqs_disabled warning from local_bh_enable
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