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Message-ID: <46EF10A2.40905@ccur.com>
Date: Mon, 17 Sep 2007 19:41:22 -0400
From: John Blackwood <john.blackwood@...r.com>
To: Roland Dreier <rdreier@...co.com>
CC: linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
Sven-Thorsten Dietrich <sdietrich@...ell.com>,
general@...ts.openfabrics.org
Subject: Re: [ofa-general] [PATCH] [WORKAROUND] CONFIG_PREEMPT_RT and ib_umad_close()
issue
Roland Dreier wrote:
> Thanks for the explanation...
>
> > But basically, with CONFIG_PREEMPT_RT enabled, the lock points, such as
> > aqcuiring a spinlock, potentially become places where the current task
> > may be context switched out / preempted.
> >
> > Therefore, when a call is made to lock a spinlock for example, the
> > caller should not currently have irqs disabled, or preemption disabled,
> > since a context switch may occur.
>
> this doesn't seem relevant here...
Hi Roland,
right. just some background info.
> > void fastcall rt_downgrade_write(struct rw_semaphore *rwsem)
> > {
> > BUG();
> > }
>
> this seems to be the problem... the -rt patch turns downgrade_write()
> into a BUG().
>
> I need to look at the locking in user_mad.c again, but I think it may
> be possible to replace both places that do downgrade_write() with
> up_write() followed by down_read().
>
> - R.
that sounds like it would be a good solution for both preempt rt and
non-preempt rt kernels.
thanks again for looking at this for us.
-
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