linux-kernel - Re: [PATCH] cdc-acm: Kill ACM

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Date:	Fri, 9 Dec 2011 19:32:04 -0800
From:	Greg KH <gregkh@...e.de>
To:	Havard Skinnemoen <hskinnemoen@...gle.com>
Cc:	alan@...ux.intel.com, davej@...hat.com, jslaby@...e.cz,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cdc-acm: Kill ACM_READY() macro completely

On Fri, Dec 09, 2011 at 04:51:54PM -0800, Havard Skinnemoen wrote:
> The ACM_READY() macro doesn't seem to do anything useful, and it may
> prevent tty_wait_until_sent() from working properly when called from
> close.
> 
> Previously, acm_tty_chars_in_buffer() returned 0 whenever
> acm->port.count was 0. This means close() could return before all the
> data has actually been written.
> 
> Signed-off-by: Havard Skinnemoen <hskinnemoen@...gle.com>
> ---
> Hi Greg,
> 
> Thanks for picking up  my patch. Unfortunately, it's not completely bug-free.
> 
> This fixes an issue I found while testing the patch: After writing something to
> /dev/ttyACM0, the process would hang for a fairly long time (10-15 seconds)
> when closing the device. This is because port.count drops to 0 before
> tty_wait_until_sent_from_close() is called, which causes ACM_READY() to return
> false, any outstanding writes never get reaped because the workqueue doesn't
> get scheduled, tty_wait_until_sent never sees any progress and eventually times
> out.
> 
> Please feel free to fold this into "cdc-acm: Fix potential deadlock (lockdep
> warning)", or let me know if you want me to send you a v2 of that patch
> instead.

I'll just apply this one, as I can't merge it together as I already
applied it.

thanks,

greg k-h
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