linux-kernel - Re: + work_on_cpu-rewrite-it-to-create-a-kernel-thread-on-demand.patch added to -mm tree

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Message-Id: <200902041428.12059.rusty@rustcorp.com.au>
Date:	Wed, 4 Feb 2009 14:28:11 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Frédéric Weisbecker <fweisbec@...il.com>,
	mingo@...e.hu, linux-kernel@...r.kernel.org, oleg@...hat.com,
	travis@....com, a.p.zijlstra@...llo.nl, mm-commits@...r.kernel.org
Subject: Re: + work_on_cpu-rewrite-it-to-create-a-kernel-thread-on-demand.patch  added to -mm tree

On Wednesday 04 February 2009 05:55:29 Andrew Morton wrote:
> On Tue, 3 Feb 2009 17:58:13 +0100
> Fr__d__ric Weisbecker <fweisbec@...il.com> wrote:
> 
> > 2009/2/3 Ingo Molnar <mingo@...e.hu>:
> > >
> > > * akpm@...ux-foundation.org <akpm@...ux-foundation.org> wrote:
> > >
> > >> ------------------------------------------------------
> > >> Subject: work_on_cpu(): rewrite it to create a kernel thread on demand
> > >> From: Andrew Morton <akpm@...ux-foundation.org>
> > >>
> > >> The various implemetnations and proposed implemetnations of work_on_cpu()
> > >> are vulnerable to various deadlocks because they all used queues of some
> > >> form.
> > >>
> > >> Unrelated pieces of kernel code thus gained dependencies wherein if one
> > >> work_on_cpu() caller holds a lock which some other work_on_cpu() callback
> > >> also takes, the kernel could rarely deadlock.
> > >>
> > >> Fix this by creating a short-lived kernel thread for each work_on_cpu()
> > >> invokation.
> > >>
> > >> This is not terribly fast, but the only current caller of work_on_cpu() is
> > >> pci_call_probe().
> > >
> > > hm, it's quite ugly as well
> 
> No it isn't.
> 
> It's no less ugly than the current code.
> 
> It's less buggy than the current code.

Whatever, I like your version.

Tho making it a series of 5 and exposing rdmsr_on_cpu/wrmsr_on_cpu for other
uses would be even better.

Thanks,
Rusty.
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