Date: Mon, 6 May 2013 16:42:48 +0200
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, Ingo Molnar <mingo@kernel.org>,
        Pavel Machek <pavel@ucw.cz>, Colin Cross <ccross@android.com>,
        Andrew Morton <akpm@osdl.org>, lkml <linux-kernel@vger.kernel.org>,
        Trond Myklebust <Trond.Myklebust@netapp.com>,
        Len Brown <len.brown@intel.com>, "Rafael J. Wysocki" <rjw@sisk.pl>,
        Ingo Molnar <mingo@redhat.com>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        "David S. Miller" <davem@davemloft.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mandeep Singh Baines <msb@chromium.org>,
        Paul Walmsley <paul@pwsan.com>, Al Viro <viro@zeniv.linux.org.uk>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        Linux PM list <linux-pm@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>, Tejun Heo <tj@kernel.org>,
        Ben Chan <benchan@chromium.org>
Subject: Re: [PATCH 2/2] lockdep: check that no locks held at freeze time
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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@chello.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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