From: Jens Axboe <axboe@suse.de>
To: "Peter T. Breuer" <ptb@it.uc3m.es>
Cc: linux kernel <linux-kernel@vger.kernel.org>
Subject: Re: what's the semaphore in requests for?
Date: Mon, 30 Jul 2001 10:24:18 +0200 [thread overview]
Message-ID: <20010730102418.G1981@suse.de> (raw)
In-Reply-To: <200107282234.f6SMY8421363@oboe.it.uc3m.es>
In-Reply-To: <200107282234.f6SMY8421363@oboe.it.uc3m.es>
On Sun, Jul 29 2001, Peter T. Breuer wrote:
> "A month of sundays ago ptb wrote:"
> > What's the semaphore field in requests for? Are driver writers supposed
> > to be using it?
>
> It seems nobody knows.
Seems you don't get mail sent to you?! I answered this on the 24th
http://asimov.lib.uaa.alaska.edu/linux-kernel/archive/2001-Week-30/0165.html
> > The reason I ask is that I've been chasing an smp bug in a block driver
> > of mine for a week. The bug only shows up in 2.4 kernels (not in same
> > code under 2.2.18) and only with smp ("nosmp" squashes it). It only
>
> I've made more progress in seeking this bug. The test is
> just dd if=/dev/mine of=/dev/null bs=4k over 2GB of data.
>
> 2 processors + 1 userspace helper daemon on device = no bug
> 2 processors + 2 userspace helper daemon on device = bug (lockup)
> 1 processors + 1 userspace helper daemon on device = no bug
> 1 processors + 2 userspace helper daemon on device = no bug
>
> Seeing this, I added a semaphore that forces the helper daemons to
> exclude each other as they enter the kernel in their ioctl calls.
> Still the lockup occurred with two processors and two daemons.
And I'll restate here what I said then too -- SHOW THE CODE! Or send me
a crystal ball and I'll be happy to solve your races for you.
--
Jens Axboe
next prev parent reply other threads:[~2001-07-30 8:22 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-07-28 22:34 what's the semaphore in requests for? Peter T. Breuer
2001-07-30 8:24 ` Jens Axboe [this message]
2001-07-30 14:14 ` Peter T. Breuer
-- strict thread matches above, loose matches on Subject: below --
2001-08-03 23:37 Peter T. Breuer
2001-07-31 18:45 Peter T. Breuer
2001-07-23 23:39 Peter T. Breuer
2001-07-24 7:44 ` Jens Axboe
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