linux-kernel - Re: [PATCH] usb: check for signals in chaoskey read function

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Date:	Tue, 16 Feb 2016 11:09:55 -0800
From:	Keith Packard <keithp@...thp.com>
To:	Oliver Neukum <oneukum@...e.com>
Cc:	linux-usb@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: check for signals in chaoskey read function

Oliver Neukum <oneukum@...e.com> writes:

> why is this needed? You are doing this right after a
> mutex_lock_interruptible().

When the device isn't contended, this mutex will never block and so
mutex_lock_interruptible will never check for a signal.

I had mistakenly assumed that usb_bulk_msg would abort when a signal was
delivered, but it doesn't.

I could be convinced that the driver should be using a different path
through the USB stack that would allow a signal to wake up while waiting
for the URB to complete, but this patch at least avoids needing to wait
for a huge read to finish. The other option would be to eliminate the
loop reading multiple URBs from the device, but that would reduce the
available bandwidth from the device pretty considerably.

-- 
-keith

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