linux-kernel - Re: [PATCH] USB: fix interrupt disabling for HCDs with shared interrupt handlers

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Message-ID: <20080701182543.GA32098@suse.de>
Date:	Tue, 1 Jul 2008 11:25:43 -0700
From:	Greg KH <gregkh@...e.de>
To:	Stefan Becker <Stefan.Becker@...ia.com>
Cc:	ext Alan Stern <stern@...land.harvard.edu>,
	linux-usb@...r.kernel.org,
	ext David Brownell <david-b@...bell.net>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	ext Leonardo Chiquitto <leonardo.lists@...il.com>
Subject: Re: [PATCH] USB: fix interrupt disabling for HCDs with shared
	interrupt handlers

On Tue, Jul 01, 2008 at 07:19:22PM +0300, Stefan Becker wrote:
> Hi Alan & Greg,
>
> third time is the charm (I hope)...
>
> ext Alan Stern wrote:
>> flags must be unsigned long.  You don't have to initialize it to 0.
>
> *Sigh* there are certain things you just shouldn't do when burning the 
> midnight oil. I changed the patch according to your suggestions and also 
> copied the comment for usb_hcd_irq() from David's changes.
>
> I hope this can still make it into 2.6.26, because it seems to solve a lot 
> of problems for the users out there...


Hm, isn't this also an issue in 2.6.25 as well?  I've had a few very
strange reports of USB just locking up in 2.6.25, could this also be the
cause there?

thanks,

greg k-h
> commit 89fa7659cb90f621513d7193b06cf19386451c33
> Author: Stefan Becker <stefan.becker@...ia.com>
> Date:   Mon Jun 30 21:18:29 2008 +0300
>
>    USB: fix interrupt disabling for HCDs with shared interrupt handlers
>       As has been discussed several times on LKML, IRQF_SHARED | 
> IRQF_DISABLED
>    doesn't work reliably, i.e. a shared interrupt handler CAN'T be certain 
> to
>    be called with interrupts disabled. Most USB HCD handlers use 
> IRQF_DISABLED
>    and therefore havoc can break out if they share their interrupt with a
>    handler that doesn't use it.
>       On my test machine the yenta_socket interrupt handler (no 
> IRQF_DISABLED)
>    was registered before ehci_hcd and one uhci_hcd instance. Therefore all
>    usb_hcd_irq() invocations for ehci_hcd and for one uhci_hcd instance
>    happened with interrupts enabled. That led to random lockups as USB core
>    HCD functions that acquire the same spinlock could be called twice
>    from interrupt handlers.
>       This patch updates usb_hcd_irq() to always disable/restore 
> interrupts.
>    usb_add_hcd() will silently remove any IRQF_DISABLED requested from HCD 
> code.
>       Signed-off-by: Stefan Becker <stefan.becker@...ia.com>

Alan and Dave, do you both ack this thing?  I know you've been involved
in creating it, just want to get the formal approval :)

thanks,

greg k-h
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