From owner-freebsd-hackers@FreeBSD.ORG  Fri Oct 28 02:54:56 2005
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Date: Thu, 27 Oct 2005 20:52:50 -0600 (MDT)
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To: dinesh@alphaque.com
From: "M. Warner Losh" <imp@bsdimp.com>
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Cc: freebsd-hackers@freebsd.org, scottl@samsco.org
Subject: Re: locking in a device driver
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In message: <4361044B.50807@alphaque.com>
            Dinesh Nair <dinesh@alphaque.com> writes:
: the userland application uses pthreads, and works like a charm both on 4.x 
: and 5.x without using the device. however, when the device is used, it 
: somehow has synchronization errors on 4.x, leading to timers (created in 
: the userland app) timing out and the like.

libc_r will block all other threads in the application while an ioctl
executes.  libpthread and libthr won't.  I've had several bugs at work
that can be traced to faulty drivers and/or faulty APIs that were
specified by people who were unaware of this issue...

Warner