linux-kernel - Re: [PATCH] IB/ehca: Allocate event queue size depending on max number of CQs and QPs

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Message-ID: <adafxt4y5kx.fsf@cisco.com>
Date:	Tue, 29 Apr 2008 09:43:42 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	Stefan Roscher <ossrosch@...ux.vnet.ibm.com>
Cc:	"LinuxPPC-Dev" <linuxppc-dev@...abs.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"OF-General" <general@...ts.openfabrics.org>,
	Roland Dreier <rolandd@...co.com>,
	"OF-EWG" <ewg@...ts.openfabrics.org>, hnguyen@...ibm.com,
	raisch@...ibm.com, fenkes@...ibm.com
Subject: Re: [PATCH] IB/ehca: Allocate event queue size depending on max number of CQs and QPs

 > 
 > Signed-off-by: Stefan Roscher <stefan.roscher at de.ibm.com>

Kind of an inadequate changelog ;)

Is this a fix or an enhancement or what?

 > +	if (atomic_read(&shca->num_cqs) >= ehca_max_cq) {

 > +	if (atomic_read(&shca->num_qps) >= ehca_max_qp) {

These are racy in the sense that multiple simultaneous calls to
create_cq/create_qp might end up exceeding the ehca_max_cq limit.  Is
that an issue?

You could close the race by using atomic_add_unless() and testing the
return value (and being careful to do atomic_dec() on error paths after
you bump num_cqs/num_qps).

 - R.
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