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Subject: Re: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U8
From: Thomas Gleixner <tglx@linutronix.de>
Reply-To: tglx@linutronix.de
To: Jens Axboe <axboe@suse.de>
Cc: Rui Nuno Capela <rncbc@rncbc.org>, Ingo Molnar <mingo@elte.hu>,
       LKML <linux-kernel@vger.kernel.org>, Lee Revell <rlrevell@joe-job.com>,
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In-Reply-To: <20041021095344.GA10531@suse.de>
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On Thu, 2004-10-21 at 11:53, Jens Axboe wrote:
> On Thu, Oct 21 2004, Thomas Gleixner wrote:
> > On Thu, 2004-10-21 at 11:12, Rui Nuno Capela wrote:
> > >  [<e018e139>] queuecommand+0x70/0x7c [usb_storage] (24)
> > 
> > As I already pointed out, this is a problem due to up(sema) in
> > queuecommand. That's one of the semaphore abuse points, which needs to
> > be fixed. 
> > 
> > The problem is that semaphores are hold by Process A and released by
> > Process B, which makes Ingo's checks trigger
> 
> That's utter crap, it's perfectly valid use.

It's not!

>From the code:

         init_MUTEX_LOCKED(&(us->sema));

This is used to wait for command completion and therefor we have the
completion API. It was used this way because the ancestor of completion
(sleep_on) was racy !

tglx




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