netdev - Re: [PATCH 2/2] lockdep: check that no locks held at freeze time

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Date:	Mon, 6 May 2013 16:42:48 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>, Pavel Machek <pavel@....cz>,
	Colin Cross <ccross@...roid.com>,
	Andrew Morton <akpm@...l.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Len Brown <len.brown@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Ingo Molnar <mingo@...hat.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mandeep Singh Baines <msb@...omium.org>,
	Paul Walmsley <paul@...an.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
	Ben Chan <benchan@...omium.org>
Subject: Re: [PATCH 2/2] lockdep: check that no locks held at freeze time

On Mon, May 06, 2013 at 07:33:28AM -0700, Linus Torvalds wrote:
> On Mon, May 6, 2013 at 1:55 AM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> >
> > Doesn't i386 have all the funny per-cpu stuff too? So the only reason it still
> > does the fugly stack based thing is because nobody could be arsed to do the
> > work of converting it.
> 
> Umm. That "fugly stack-based" thing is better than the per-cpu crap.
> 
> The percpu stuff implies a memory load. The stack based thing gets
> thread_info with pure register accesses. Much better.
> 
> For "current()" the per-cpu thing may be better, but if you actually
> need the thread-info (not the case here, but in other places), the
> stack masking is superior when it works (ie when you don't have
> multi-stack issues due to irq's etc)

But you can do both right? Use per-cpu for current and stack frobbery for
current_thread_info().

That said, ISTR some risky bits where the stack frobbery went awry due to
irq-stacks which is the source for my feelings towards the stack frobbery.

That and of course that i386 and x86-64 behave differently for no apparent
reason.
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