Re: [PATCH] hid: usbhid: fix possible deadlock in __usbhid_submit_report

From: Alan Stern <stern@rowland.harvard.edu>
To: Ming Lei <ming.lei@canonical.com>
Cc: Oliver Neukum <oliver@neukum.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Kosina <jkosina@suse.cz>,
	linux-usb@vger.kernel.org, linux-input@vger.kernel.org,
	stable@vger.kernel.org
Subject: Re: [PATCH] hid: usbhid: fix possible deadlock in __usbhid_submit_report
Date: Sat, 21 Apr 2012 13:31:20 -0400 (EDT)	[thread overview]
Message-ID: <Pine.LNX.4.44L0.1204211327090.475-100000@netrider.rowland.org> (raw)
In-Reply-To: <CACVXFVPR76O+zFtL3pBc-KyhN85xN6AkgTT_Md1kG2wWwjosiw@mail.gmail.com>

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On Sat, 21 Apr 2012, Ming Lei wrote:

> >> Think about what happens if the URB being unlinked hasn't been
> >> presented to the hardware yet.  Once it has been removed from the HCD's
> >> internal lists, there's no reason not to give it back right away.  And
> >> there's no natural time to give it back later.
> >
> > Now. The question is not when, but from which context.
> > The context should be uniform, so that the requirements
> > for locking should also be uniform.
> 
> How about always scheduling a tasklet to run what usb_unlink_urb does?
> just implement usb_unlink_urb as something like
> tasklet_schedule(unlink_tasklet).
> 
> Then we can have a uniform lock requirement and no changes are involved
> on host controller drivers.

The return values would not be correct.

On the other hand, usbnet could call usb_unlink_urb from within a 
tasklet.

Alan Stern

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