linux-kernel - Re: [PATCH 0/9] usb: musb: several bugfixes for the musb driver

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Message-ID: <20140721151140.GG6852@saruman.home>
Date:	Mon, 21 Jul 2014 10:11:40 -0500
From:	Felipe Balbi <balbi@...com>
To:	Lothar Waßmann <LW@...O-electronics.de>
CC:	<balbi@...com>, Ezequiel Garcia <ezequiel@...guardiasur.com.ar>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>,
	George Cherian <george.cherian@...com>,
	<linux-arm-kernel@...ts.infradead.org>,
	Roger Quadros <rogerq@...com>
Subject: Re: [PATCH 0/9] usb: musb: several bugfixes for the musb driver

On Mon, Jul 21, 2014 at 09:34:30AM +0200, Lothar Waßmann wrote:
> Hi,
> 
> Felipe Balbi wrote:
> > Hi,
> > 
> > On Fri, Jul 18, 2014 at 01:16:36PM -0300, Ezequiel Garcia wrote:
> > > Hi Lothar,
> > > 
> > > On 18 Jul 11:31 AM, Lothar Waßmann wrote:
> > > > The first three patches do some source code cleanup in the files that
> > > > are modified in the subsequent patches.
> > > > 
> > > 
> > > I've applied patches 4 and 9 on a recent -next, after fixing a conflict
> > > due to patch 3 ("usb: musb_am335x: source cleanup"):
> > > 
> > > > Patch 4 carries the proper fix reported in commit:
> > > >         7adb5c876e9c ("usb: musb: Fix panic upon musb_am335x module removal")
> > > > 
> > > > Patch 9 reinstates module unloading support for the musb_am335x driver
> > > >         which was disabled due to a false failure analysis
> > > > 
> > > 
> > > For these two patches, Tested-by: Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
> > > 
> > > Tested on a beaglebone with a mass storage USB device, module load/unload
> > > works without issues. The module_get/put in the phy is now preventing the
> > > musb_am335x driver unload, which seems to be the real cause of the issue
> > > I reported. Thanks for providing a proper fix!
> > 
> > I don't that's a good fix. The problem is that even after am335x
> > removing all its child, someone else tried to release the PHY. That
> > ordering is the one that needs to be fixed. Doing a module_get on the
> > parent device looks like a hack to me.
> > 
> No. It guarantees that the module cannot be unloaded when its resources
> are still in use!

it's still a hack. You have a child incrementing the usage count on its
parent just because a sibbling isn't doing the right thing.

-- 
balbi

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