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Re: [ofa-general] [PATCH] [WORKAROUND] CONFIG_PREEMPT_RT and ib_umad_close() issue

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From: Roland Dreier <rdreier@...>
To: John Blackwood <john.blackwood@...>
Cc: <linux-rt-users@...>, <linux-kernel@...>, <general@...>, Sven-Thorsten Dietrich <sdietrich@...>
Subject: Re: [ofa-general] [PATCH] [WORKAROUND] CONFIG_PREEMPT_RT and ib_umad_close() issue
Date: Monday, September 17, 2007 - 11:56 am

> 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.

 - R.
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Messages in current thread:
[PATCH] [WORKAROUND] CONFIG_PREEMPT_RT and ib_umad_close() i..., John Blackwood, (Mon Sep 17, 11:22 am)
Re: [ofa-general] [PATCH] [WORKAROUND] CONFIG_PREEMPT_RT and..., Roland Dreier, (Mon Sep 17, 11:56 am)
Re: [ofa-general] [PATCH] [WORKAROUND] CONFIG_PREEMPT_RT and..., Daniel Walker, (Mon Sep 17, 1:07 pm)