linux-kernel - Re: [PATCH v3 2/3] hvc_init(): Enforce one-time initialization.

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Message-ID: <874nybqo0o.fsf@rustcorp.com.au>
Date:	Fri, 11 Nov 2011 15:00:31 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Miche Baker-Harvey <miche@...gle.com>,
	Greg Kroah-Hartman <gregkh@...e.de>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	xen-devel@...ts.xensource.com,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Anton Blanchard <anton@...ba.org>,
	Amit Shah <amit.shah@...hat.com>,
	Mike Waychison <mikew@...gle.com>,
	ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	Eric Northrup <digitaleric@...gle.com>
Subject: Re: [PATCH v3 2/3] hvc_init():  Enforce one-time initialization.

On Tue, 08 Nov 2011 13:45:04 -0800, Miche Baker-Harvey <miche@...gle.com> wrote:
> hvc_init() must only be called once, and no thread should continue with hvc_alloc()
> until after initialization is complete.  The original code does not enforce either
> of these requirements.  A new mutex limits entry to hvc_init() to a single thread,
> and blocks all later comers until it has completed.
> 
> This patch fixes multiple crash symptoms.

No, it doesn't: not now your previous double-hvc_init patch has been
reverted.

It's easy to show this is the case though: replace mutex_lock() with:

        if (!mutex_trylock()) {
                WARN(1, "hvc_console: mutex is stopping us!\n");
                mutex_lock();
        }

If you get that warning, then your mutex is doing something.

Thanks,
Rusty.
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