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Message-ID: <alpine.LFD.2.02.1104111658560.1770@c4eb>
Date: Mon, 11 Apr 2011 17:05:08 +0200 (CEST)
From: Sebastian Ott <sebott@...ux.vnet.ibm.com>
To: Greg KH <gregkh@...e.de>
cc: linux-kernel@...r.kernel.org
Subject: Re: sysfs: cannot create duplicate filename
On Mon, 11 Apr 2011, Greg KH wrote:
> On Mon, Apr 11, 2011 at 04:33:03PM +0200, Sebastian Ott wrote:
> > On Mon, 11 Apr 2011, Greg KH wrote:
> >
> > > On Mon, Apr 11, 2011 at 04:04:08PM +0200, Sebastian Ott wrote:
> > > > Hi,
> > > >
> > > > i've seen this warning which looks to be caused by a race between device_add
> > > > and driver_register
> > > >
> > > > [ 80.893594] sysfs: cannot create duplicate filename '/bus/ccw/drivers/qeth/0.0.b57d'
> > >
> > > Isn't the problem here the fact that you are creating 2 directories of
> > > the same name?
> > I'm sure this isn't the case here. The bus code just calls device_add and
> > at the same time on a different thread a module is loaded which registers
> > a driver at the bus.
> >
> > I was able to reproduce this with a module which creates a dummy bus
> > and registers drivers and devices on this bus on 2 different workqueues.
>
> That makes sense, as no bus should be doing this on multiple "threads".
> What real-life bus does this today?
A bus that will recognize and register a lot of devices, after the first
uevent is presented to userspace, a module will be loaded registering a
driver from a different thread. I don't think thats uncommon.
>
> > > > [ 80.893611] ------------[ cut here ]------------
> > > > [ 80.893614] WARNING: at /home/autobuild/BUILD/linux-2.6.38.2-20110404/fs/sysfs/dir.c:455
> > > > [ 80.893617] Modules linked in: qeth ccwgroup
> > > > [ 80.893623] Modules linked in: qeth ccwgroup
> > > > [ 80.893629] CPU: 1 Not tainted 2.6.38.2-48.x.20110404-s390xdefault #1
> > > > [ 80.893632] Process kworker/u:1 (pid: 25, task: 000000007e6c5a40, ksp: 000000007e6cb980)
> > > > [ 80.893635] Krnl PSW : 0704000180000000 00000000002b676c (sysfs_add_one+0xd0/0xe8)
> > > > [ 80.893643] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:0 CC:0 PM:0 EA:3
> > > > [ 80.893647] Krnl GPRS: 00000000000000bd 0000000000000000 000000000000005e 0000000000000001
> > > > [ 80.893651] 0000000000589daa 00000000005a1248 0000000000000000 0000000000000000
> > > > [ 80.893654] 0000000000000000 0000000000000001 000000007865c000 000000007e6cbbd8
> > > > [ 80.893657] 000000007c704398 00000000ffffffef 00000000002b6768 000000007e6cbb00
> > > > [ 80.893668] Krnl Code: 00000000002b675c: c0200020041d larl %r2,6b6f96
> > > > [ 80.893672] 00000000002b6762: c0e500169afb brasl %r14,589d58
> > > > [ 80.893676] 00000000002b6768: a7f40001 brc 15,2b676a
> > > > [ 80.893680] >00000000002b676c: b904002a lgr %r2,%r10
> > > > [ 80.893684] 00000000002b6770: c0e5fffb6236 brasl %r14,222bdc
> > > > [ 80.893687] 00000000002b6776: a7f4ffad brc 15,2b66d0
> > > > [ 80.893692] 00000000002b677a: e320c0480004 lg %r2,72(%r12)
> > > > [ 80.893695] 00000000002b6780: a7f4ffec brc 15,2b6758
> > > > [ 80.893699] Call Trace:
> > > > [ 80.893701] ([<00000000002b6768>] sysfs_add_one+0xcc/0xe8)
> > > > [ 80.893705] [<00000000002b7046>] sysfs_do_create_link+0xda/0x268
> > > > [ 80.893708] [<0000000000409f26>] driver_sysfs_add+0x66/0xcc
> > > > [ 80.893713] [<000000000040a0a2>] device_bind_driver+0x26/0x48
> > > > [ 80.893717] [<000000000040a110>] device_attach+0x4c/0xd4
> > > > [ 80.893720] [<0000000000409734>] bus_probe_device+0x4c/0x5c
> > > > [ 80.893724] [<0000000000406c52>] device_add+0x61e/0x73c
> > > > [ 80.893728] [<00000000004631a6>] ccw_device_todo+0x31a/0x380
> > > > [ 80.893733] [<000000000015f5b6>] process_one_work+0x1f6/0x4f0
> > > > [ 80.893739] [<0000000000163358>] worker_thread+0x17c/0x370
> > > > [ 80.893742] [<00000000001690ca>] kthread+0xa6/0xb0
> > > > [ 80.893747] [<000000000058f5f2>] kernel_thread_starter+0x6/0xc
> > > > [ 80.893752] [<000000000058f5ec>] kernel_thread_starter+0x0/0xc
> > > > [ 80.893756] 4 locks held by kworker/u:1/25:
> > > > [ 80.893758] #0: (cio){++++.+}, at: [<000000000015f524>] process_one_work+0x164/0x4f0
> > > > [ 80.893766] #1: ((&cdev->private->todo_work)){+.+.+.}, at: [<000000000015f524>] process_one_work+0x164/0x4f0
> > > > [ 80.893773] #2: (&__lockdep_no_validate__){+.+.+.}, at: [<000000000040a0fc>] device_attach+0x38/0xd4
> > > > [ 80.893780] #3: (sysfs_mutex){+.+.+.}, at: [<00000000002b7030>] sysfs_do_create_link+0xc4/0x268
> > > > [ 80.893787] Last Breaking-Event-Address:
> > > > [ 80.893790] [<00000000002b6768>] sysfs_add_one+0xcc/0xe8
> > > > [ 80.893795] ---[ end trace ded2f91fcf2c6165 ]---
> > > >
> > > >
> > > > * device_add attached the device to the bus /*break*/
> > > > * driver_register walks the list of devices and tries to bind
> > > > unbound devices
> > > > * /*continue*/ device_add calls device_attach which gets confused
> > > > that the device is already bound to a driver
> > >
> > > Why would your bus code ever allow this to happen? It's the caller's
> > > responsiblity to do things in the correct order, right?
> > I don't think the bus code which calls device_register can (or should)
> > prevent drivers from beeing registered at this bus at the same time.
>
> Why not? That's the way all kernel subsystems work today that I know
> of. Has this changed?
What about an exported bus_type? At all time a driver for this bus can
be registered, the bus code has no chance to prevent or serialize this.
>
> thanks,
>
> greg k-h
>
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