linux-kernel - Re: [PATCH] serial: revert "Use block_til

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Date:	Sat, 19 Jun 2010 22:57:06 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Tony Luck <tony.luck@...el.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, Greg KH <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	John Kacur <jkacur@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] serial: revert "Use block_til_ready helper"

O> I could reproduce the problem now and bisected it down to a cleanup
> patch that can fortunately get reverted. The symptom that I saw
> is that when I open a serial port for the second time (e.g. starting
> getty and logging in), the output gets garbled, while the first one
> worked fine. This does not rely on the console code at all.

So the init code isn't getting run somewhere for some reason. Almost
certainly a count bug.

> Alan, any idea where the problem may be with the broken patch?

I'll take a look. We really don't want to revert this as it fixes some
nasty things the BKL covers over so I'd be worried the races would become
exposed (and it possibly allows NULL->func() calls if it can which would
be bad)

First guess would be something in port->count going astray and the port
not getting re-initialised.

Important question - does it need a getty or will a simple cat < /dev/foo
twice get garbled (or cat > if its garbling the other way)

Which direction matters and whether a hangup is needed matters
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