linux-kernel - Re: [PATCH -mm v4 6/9] atmel_serial: Split the interrupt handler

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Date:	Wed, 30 Jan 2008 13:36:59 +0100
From:	Haavard Skinnemoen <hskinnemoen@...el.com>
To:	michael <trimarchi@...dalf.sssup.it>
Cc:	Remy Bohmer <linux@...mer.net>, fabio@...dalf.sssup.it,
	Andrew Victor <linux@...im.org.za>,
	Chip Coldwell <coldwell@...hat.com>,
	Marc Pignat <marc.pignat@...s.ch>,
	David Brownell <david-b@...bell.net>,
	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH -mm v4 6/9] atmel_serial: Split the interrupt handler

On Wed, 30 Jan 2008 11:29:59 +0100
michael <trimarchi@...dalf.sssup.it> wrote:
> > Now, _that_ is strange. I can't see anything that needs protection
> > across that call; in fact, I think we can lock a lot less than what we
> > currently do.
> >
> >   
> I explain it bad:
> - with spin_lock the system seems, there is no problem with Valuntary 
> Preeption and
> Preemptible Kernel
> - with full preemption  it runs but the serial line can't be used for 
> receiving at
> high bit rate (using lrz)

...but if you drop the spinlock across the call to
tty_flip_buffer_push, you get an Oops?

Could you post the Oops?

> >> Complete Preemption (Real-Time) ok but the serials is just unusable due
> >> to too many overruns (just using lrz)
> >>     
> >
> > Is it worse than before? IIRC Remy mentioned something about
> > IRQF_NODELAY being the reason for moving all this code to softirq
> > context in the first place; does the interrupt handler run in hardirq
> > context?
> >
> >   
> In the complete preemption yes.

Which question did you answer "yes" to? That it's worse than before or
that the interrupt handler runs in hardirq context (i.e. IRQF_NODELAY)?

> > I think you're right. Can you change it and see if it helps?
> >
> >   
> I just change it because I have corruption on receiving buffer. All
> my test are done with this fix

Ok.

> > I guess I didn't test it thoroughly enough with DMA
> > disabled...slub_debug ought to catch such things, but not until we
> > receive enough data to actually overflow the buffer.
> >
> >   
> I just test it I don't have
> buffer overflow.

No, I'd expect your allocation fix to take care of that. Or did you by
any chance test without the fix and with slub_debug enabled?

> I protect with a spinlock the access to the register when we sending
> from the tasklet. It is correct?

I have no idea. Could you post some more specifics about what you
modified, for example a diff?

Most of the tasklet is already protected by the spinlock, so you must
be careful to avoid any lock recursion.

Haavard
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