From: Daniel Walker <dwalker@mvista.com>
To: Roland Dreier <rdreier@cisco.com>
Cc: John Blackwood <john.blackwood@ccur.com>,
linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org,
general@lists.openfabrics.org,
Sven-Thorsten Dietrich <sdietrich@novell.com>
Subject: Re: [ofa-general] [PATCH] [WORKAROUND] CONFIG_PREEMPT_RT and ib_umad_close() issue
Date: Mon, 17 Sep 2007 10:07:56 -0700 [thread overview]
Message-ID: <1190048876.3253.41.camel@imap.mvista.com> (raw)
In-Reply-To: <adaps0hnv5a.fsf@cisco.com>
On Mon, 2007-09-17 at 08:56 -0700, Roland Dreier wrote:
> > When using OFED-1.2.5 based infiniband kernel modules on 2.6.22 based
> > kernels with the Ingo Molnar CONFIG_PREEMPT_RT applied, then commands
> > such as ibnetdiscvoer, smpquery, sminfo, etc. will hang. The problem
> > is with the downgrade_write() rw semaphore usage in the
> > ib_umad_close() routine.
>
> Can you give a few more details on how PREEMPT_RT changes locking
> rules (or just exposes existing bugs maybe?) so that the
> downgrade_write() causes the issue? I would like to fix this cleanly
> but I don't really understand what the problem is.
the read/write semaphore functionality is basically reduced to just a
binary semaphore , i.e. one reader, or one writer . I think the BUG();
in downgrade_write() is likely part of a removal plan for
downgrade_write() (that's just a guess tho)
Daniel
next prev parent reply other threads:[~2007-09-17 17:10 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-09-17 15:22 John Blackwood
2007-09-17 15:56 ` [ofa-general] " Roland Dreier
2007-09-17 17:07 ` Daniel Walker [this message]
2007-09-17 17:19 John Blackwood
2007-09-17 21:40 ` Roland Dreier
2007-09-17 23:41 ` John Blackwood
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