From: Daniel Phillips <phillips@bonn-fries.net>
To: Robert Love <rml@tech9.net>,
Emmanuel Michon <emmanuel_michon@realmagic.fr>
Cc: linux-kernel@vger.kernel.org
Subject: Re: spinlocking between user context / tasklet / tophalf question
Date: Sun, 28 Apr 2002 00:52:08 +0200 [thread overview]
Message-ID: <E171b32-0001QJ-00@starship> (raw)
In-Reply-To: <7wwuuu4zam.fsf@avalon.france.sdesigns.com> <1019848780.2045.617.camel@phantasy>
Hi Robert,
On Friday 26 April 2002 21:19, Robert Love wrote:
> On Fri, 2002-04-26 at 04:52, Emmanuel Michon wrote:
> > 2. What is the reality behind: ``things which sleep'', is it really a problem
> > to use copy_from_user/copy_to_user holding a spinlock?
>
> Yes, they sleep.
Well, I think he really wanted to know why it's bad. Emmanuel, suppose process A
takes spinlock S then sleeps. Process B is then scheduled and tries to acquire
S - bang, deadlock: Process A can't release the spinlock because it's sleeping.
Let alone the fact that another CPU trying to acquire S is going to end up
stalled potentially many milliseconds before process A wakes up again and
releases the spinlock.
--
Daniel
prev parent reply other threads:[~2002-04-28 22:51 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-04-26 8:52 spinlocking between user context / tasklet / tophalf question Emmanuel Michon
2002-04-26 16:33 ` george anzinger
2002-04-27 19:13 ` Alan Cox
2002-04-26 19:19 ` Robert Love
2002-04-27 22:52 ` Daniel Phillips [this message]
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