Subject: Re: [BUG][2.6.8.1] serial driver hangs SMP kernel, but not the UP
	kernel
From: Paul Fulghum <paulkf@microgate.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Russell King <rmk+lkml@arm.linux.org.uk>, Tim_T_Murphy@Dell.com,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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	 <20041029212029.I31627@flint.arm.linux.org.uk>
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Date: Sat, 30 Oct 2004 19:26:23 -0500
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On Sat, 2004-10-30 at 17:43, Alan Cox wrote:
> On Sad, 2004-10-30 at 00:40, Paul Fulghum wrote:
> > Would it make sense to do something like (in tty_io.c) the following?
> 
> Not really because it can legally occur if you flip the low latency
> flag while a transaction is queued. It might work if you waited for
> scheduled work to complete in the flag changing.

I don't see how having flush_to_ldisc() queued
or already running (on another processor) negates
the prohibition on calling tty_flip_buffer_push()
with low_latency set in interrupt context.

The comments for tty_flip_buffer_push() state the
function should not be called in interrupt context
if low_latency is set (no exceptions are listed).
Meaning flush_to_ldisc() should only be called
in process context.

If flush_to_ldisc() is queued or already executing,
there is no protection against calling
flush_to_ldisc() again, directly in interrupt context.
TTY_DONT_FLIP is no protection, that is only set
in read_chan() of n_tty.c

If I'm missing something, please point it out.

-- 
Paul Fulghum
paulkf@microgate.com


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