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To: Zach Brown <zach.brown@oracle.com>
Cc: Ingo Molnar <mingo@elte.hu>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       openib-general@openib.org, Arjan van de Ven <arjan@infradead.org>
Subject: Re: [openib-general] ipoib lockdep warning
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From: Roland Dreier <rdreier@cisco.com>
Date: Tue, 11 Jul 2006 17:06:10 -0700
In-Reply-To: <44B439F7.3090008@oracle.com> (Zach Brown's message of "Tue, 11 Jul 2006 16:53:27 -0700")
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 > > So, ugh... maybe the best thing to do is change lib/idr.c to use
 > > spin_lock_irqsave() internally?
 > 
 > I dunno, it seems to have had _irq() locking in the past?  From the
 > comment at the top:
 > 
 >  * Modified by George Anzinger to reuse immediately and to use
 >  * find bit instructions.  Also removed _irq on spinlocks.

Well, _irq would be no good, because we might want to call idr stuff
with interrupts disabled.  But making idr internally _irqsave seems
like the right fix to me.

I think the real issue here is that the sa_query.c stuff wants to use
the idr mechanism to assign "query ids", and other modules want to be
able to start queries from any context.  So if idr uses bare spin_lock
internally, then sa_query.c has no choice but to wrap all idr calls
inside spin_lock_irqsave and do all allocation with GFP_ATOMIC, which
doesn't seem very nice.

 - R.