linux-kernel - Re: [PATCH] Fix SMP alternatives : use mutex instead of spinlock, text

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Date:	Thu, 1 May 2008 16:08:59 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Luca Tettamanti <kronos.it@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix SMP alternatives : use mutex instead of spinlock,
	text_poke is sleepable

* Linus Torvalds (torvalds@...ux-foundation.org) wrote:
> 
> 
> On Thu, 1 May 2008, Mathieu Desnoyers wrote:
> > 
> > Yep. I think using a mutex should fix it. There is no reason to use a
> > spinlock rather than a mutex here.
> 
> Is there any reason to do any locking what-so-ever?
> 
> If this code could possibly race with something else, that sounds like a 
> bug in itself, no?
> 
> 		Linus

The smp_alt mutex taken in
alternatives_smp_module_add/alternatives_smp_module_del seems required
because this code will run at module load/free, even in SMP context (not
within stop_machine_run).

As for alternatives_smp_switch, which is called when switching between
UP and SMP, always in UP context, I guess we should assume it could be
executed concurrently wrt the module_load/free, even in UP on a
CONFIG_PREEMPT kernel.

Mathieu


-- 
Mathieu Desnoyers
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