linux-kernel - Re: [PATCH] usb/core/devio.c: Don't use GFP_KERNEL while we cannot reset a storage device

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Message-ID: <Pine.LNX.4.44L0.1303111450550.2246-100000@iolanthe.rowland.org>
Date:	Mon, 11 Mar 2013 14:55:51 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ming Lei <tom.leiming@...il.com>
cc:	Alexey Khoroshilov <khoroshilov@...ras.ru>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Hans de Goede <hdegoede@...hat.com>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<ldv-project@...uxtesting.org>
Subject: Re: [PATCH] usb/core/devio.c: Don't use GFP_KERNEL while we cannot
 reset a storage device

On Tue, 12 Mar 2013, Ming Lei wrote:

> > In general it isn't, no.  But usbfs uses the lock to prevent races with
> > driver_disconnect() -- it is invalid to submit URBs after the
> > disconnect routine has returned.
> 
> If so, we may introduce another lock to avoid the race.
> 
> So I think we may figure out to decrease the device lock
> scope in devio.c, and most of ioctl commands might not require it
> at all, then the problem addressed by the patch can be fixed too.

That might work.  A mutex could be added to the dev_state structure.  
The mutex would be locked whenever an URB was being submitted and
during driver_disconnect, and perhaps a few other places too, but not
when memory was being allocated.  The device itself would remain 
unlocked most of the time.

Alan Stern

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