linux-kernel - Re: 2.6.18-rc5-mm1 + all hotfixes -- INFO: possible recursive locking detected

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Date:	Wed, 06 Sep 2006 18:50:48 +0200
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Greg KH <gregkh@...e.de>
CC:	Andrew Morton <akpm@...l.org>, Miles Lane <miles.lane@...il.com>,
	linux1394-devel@...ts.sourceforge.net,
	LKML <linux-kernel@...r.kernel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Ben Collins <bcollins@...ntu.com>
Subject: Re: 2.6.18-rc5-mm1 + all hotfixes -- INFO: possible recursive	locking
 detected

I wrote:
> I wrote:
>> Or maybe it's older. Nodemgr takes class->subsys.rwsem and
>> device.bus->subsys.rwsem. It always did. Could there be a change in
>> driver core which makes this recursive? Or has it always been recursive?
>> For example,
>>
>> static void nodemgr_update_pdrv(struct node_entry *ne)
>> {
>> 	struct unit_directory *ud;
>> 	struct hpsb_protocol_driver *pdrv;
>> 	struct class *class = &nodemgr_ud_class;
>> 	struct class_device *cdev;
>>
>> 	down_read(&class->subsys.rwsem);
>> 	list_for_each_entry(cdev, &class->children, node) {

This may be wrong anyway. According to include/linux/device.h,
class->sem should be used to protect access to class->children. There
are more places in nodemgr of this sort.

>> 		ud = container_of(cdev, struct unit_directory, class_dev);
>> 		if (ud->ne != ne || !ud->device.driver)
>> 			continue;
>>
>> 		pdrv = container_of(ud->device.driver, struct hpsb_protocol_driver, driver);
>>
>> 		if (pdrv->update && pdrv->update(ud)) {
>> 			down_write(&ud->device.bus->subsys.rwsem);
>> 			device_release_driver(&ud->device);
>> 			up_write(&ud->device.bus->subsys.rwsem);
>> 		}
>> 	}
>> 	up_read(&class->subsys.rwsem);
>> }
> 
> Hi Greg,
> 
> perhaps you could advise on this. It appears from grepping through the
> sources that drivers/ieee1394/nodemgr.c is the only one with mixed
> access to device.bus->subsys.rwsem and class->subsys.rwsem.
> 
> Other usages of subsys.rwsem that I found are:
> 1a.) dev->bus->subsys.rwsem
> driver/ide/ide-proc.c and drivers/net/phy/phy_device.c take
> dev->bus->subsys.rwsem. drivers/pnp/card.c takes dev.bus->subsys.rwsem.
> 
> 1b.) driver.bus->subsys.rwsem
> drivers/s390/net/qeth_proc.c takes driver.bus->subsys.rwsem.
> 
> 2.) class->subsys.rwsem
> drivers/scsi/hosts.c takes class->subsys.rwsem.
> 
> 3.) bustype.subsys.rwsem
> drivers/input/serio/serio.c takes serio_bus.subsys.rwsem.
> drivers/input/gameport/gameport.c takes gameport_bus.subsys.rwsem.
> drivers/base/power/shutdown.c takes devices_subsys.rwsem.
> drivers/usb/core/devices.c and devio.c take usb_bus_type.subsys.rwsem.
> 
> Do class->subsys.rwsem, bus->subsys.rwsem, and bus_type.subsys.rwsem
> point to identical or different lock instances?
> 
> Either way, could it hurt to convert nodemgr to uniformly use
> ieee1394_bus_type.subsys.rwsem all over the place?
> 
> Thanks,


-- 
Stefan Richter
-=====-=-==- =--= --==-
http://arcgraph.de/sr/
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