Subject: Re: [patch] Real-Time Preemption, -RT-2.6.12-rc1-V0.7.41-07
From: Steven Rostedt <rostedt@goodmis.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: LKML <linux-kernel@vger.kernel.org>
In-Reply-To: <20050331174927.GA11483@elte.hu>
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Organization: Kihon Technologies
Date: Thu, 31 Mar 2005 19:59:33 -0500
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Hi Ingo,

I was wondering if the issue the bit_spin_lock has gone into the side
burner? I understand that this is a major problem to change it, if you
want to get into the mainline kernel. But I still believe it to be a
problem. With kjournald spinning on a bit lock until it finishes it's
quota, can be bad for latencies. 

Although it only deadlocks on your system if it was a real-time task, it
still has the ability to become one. Since it can hold two different
locks at the time of the spin, if a rt-task tries to grab it, with
priority inheritance it becomes rt, and if that just happened to be the
highest priority task on the system, you just created a deadlock.

It's not so much of an issue with me, since I'm working with a parallel
kernel, and have implemented my earlier fixes to it. I just wanted to
know if there's any plan to deal with them on your end.  I do see this
causing a random lockup once in a while, and wanted the user to beware.
Of course if you just avoid ext3, you wont have a problem.

-- Steve


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