sysfs: cannot create duplicate filename

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'
[ 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

to fix this we could:
* hold the device lock in device_add (from bus_add_device to
bus_probe_device) ..but this means we have to extract the lock
from the inside of some of these functions and i'm not sure about
holding the lock while the blocking_notifier_call_chain thing..

* add a bus mutex, preventing concurrent registrations of devices
and drivers to a bus

* change device_attach to detect an already bound device..something
like the following:

regards,
Sebastian
-----

Add a check to device_attach to identify an already bound device.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
---
drivers/base/dd.c | 5 +++++
1 file changed, 5 insertions(+)

--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -245,6 +245,10 @@ int device_attach(struct device *dev)

device_lock(dev);
if (dev->driver) {
+ if (klist_node_attached(&dev->p->knode_driver)) {
+ ret = 1;
+ goto out_unlock;
+ }
ret = device_bind_driver(dev);
if (ret == 0)
ret = 1;
@@ -257,6 +261,7 @@ int device_attach(struct device *dev)
ret = bus_for_each_drv(dev->bus, NULL, dev, __device_attach);
pm_runtime_put_sync(dev);
}
+out_unlock:
device_unlock(dev);
return ret;
}
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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?


> [ 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?

> to fix this we could:
> * hold the device lock in device_add (from bus_add_device to
> bus_probe_device) ..but this means we have to extract the lock
> from the inside of some of these functions and i'm not sure about
> holding the lock while the blocking_notifier_call_chain thing..
>
> * add a bus mutex, preventing concurrent registrations of devices
> and drivers to a bus
>
> * change device_attach to detect an already bound device..something
> like the following:

How about fix your caller code?

thanks,

greg k-h
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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.

>
>
> > [ 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.

>
> > to fix this we could:
> > * hold the device lock in device_add (from bus_add_device to
> > bus_probe_device) ..but this means we have to extract the lock
> > from the inside of some of these functions and i'm not sure about
> > holding the lock while the blocking_notifier_call_chain thing..
> >
> > * add a bus mutex, preventing concurrent registrations of devices
> > and drivers to a bus
> >
> > * change device_attach to detect an already bound device..something
> > like the following:
>
> How about fix your caller code?
>
> thanks,
>
> greg k-h
>
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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?

> > > [ 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?

thanks,

greg k-h
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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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On Mon, Apr 11, 2011 at 05:05:08PM +0200, Sebastian Ott wrote:
>
>
> 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.

But again, what kernel code today does this? I think they all have
locks to keep this from happening, right?

> > > > > * 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.

No, the bus core is the one that should be binding the bus type to the
driver and doing the registering. No individual driver should ever be
messing with a bus_type at all.

Now perhaps platform devices are, and if so, we might want to resolve
this, but no "real" bus should ever be doing this.

thanks,

greg k-h
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On Mon, 11 Apr 2011, Greg KH wrote:

> On Mon, Apr 11, 2011 at 05:05:08PM +0200, Sebastian Ott wrote:
> >
> >
> > 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.
>
> But again, what kernel code today does this? I think they all have
> locks to keep this from happening, right?
I couldn't find a bus who protects device_register against driver_register
and I don't think this is something which should be handled by every
individual bus but from within the driver core.

>
> > > > > > * 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.
>
> No, the bus core is the one that should be binding the bus type to the
> driver and doing the registering. No individual driver should ever be
> messing with a bus_type at all.
>
> Now perhaps platform devices are, and if so, we might want to resolve
> this, but no "real" bus should ever be doing this.
>
> thanks,
>
> greg k-h
>
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On Mon, Apr 11, 2011 at 07:50:34PM +0200, Sebastian Ott wrote:
>
>
> On Mon, 11 Apr 2011, Greg KH wrote:
>
> > On Mon, Apr 11, 2011 at 05:05:08PM +0200, Sebastian Ott wrote:
> > >
> > >
> > > 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.
> >
> > But again, what kernel code today does this? I think they all have
> > locks to keep this from happening, right?
> I couldn't find a bus who protects device_register against driver_register
> and I don't think this is something which should be handled by every
> individual bus but from within the driver core.

How did you cause the oops in this original message? What type of bus
was it on? And did your patch solve the issue?

thanks,

greg k-h
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On Mon, 11 Apr 2011, Greg KH wrote:

> On Mon, Apr 11, 2011 at 07:50:34PM +0200, Sebastian Ott wrote:
> >
> >
> > On Mon, 11 Apr 2011, Greg KH wrote:
> >
> > > On Mon, Apr 11, 2011 at 05:05:08PM +0200, Sebastian Ott wrote:
> > > >
> > > >
> > > > 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.
> > >
> > > But again, what kernel code today does this? I think they all have
> > > locks to keep this from happening, right?
> > I couldn't find a bus who protects device_register against driver_register
> > and I don't think this is something which should be handled by every
> > individual bus but from within the driver core.
>
> How did you cause the oops in this original message? What type of bus
> was it on? And did your patch solve the issue?

I've seen this warning on a system which had a lot of devices attached.
Those devices also responded _very_ slow. So it took some time to
register all these deivces (qeth) on the bus (ccw). During this time
the qeth module got loaded and registered the qeth driver.

Since i've never seen this warning and those devices normally don't
take so much time to respond I wrote the beforementioned module to
reproduce the race and make sure that this is no driver issue.

With this module the warning could be triggered after a few cycles.
With the patch applied, I did not see the warning again even after
> 10.000 cycles.

regards,
Sebastian
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On Tue, Apr 12, 2011 at 04:39:49PM +0200, Sebastian Ott wrote:
>
>
> On Mon, 11 Apr 2011, Greg KH wrote:
>
> > On Mon, Apr 11, 2011 at 07:50:34PM +0200, Sebastian Ott wrote:
> > >
> > >
> > > On Mon, 11 Apr 2011, Greg KH wrote:
> > >
> > > > On Mon, Apr 11, 2011 at 05:05:08PM +0200, Sebastian Ott wrote:
> > > > >
> > > > >
> > > > > 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.
> > > >
> > > > But again, what kernel code today does this? I think they all have
> > > > locks to keep this from happening, right?
> > > I couldn't find a bus who protects device_register against driver_register
> > > and I don't think this is something which should be handled by every
> > > individual bus but from within the driver core.
> >
> > How did you cause the oops in this original message? What type of bus
> > was it on? And did your patch solve the issue?
>
> I've seen this warning on a system which had a lot of devices attached.
> Those devices also responded _very_ slow. So it took some time to
> register all these deivces (qeth) on the bus (ccw). During this time
> the qeth module got loaded and registered the qeth driver.
>
> Since i've never seen this warning and those devices normally don't
> take so much time to respond I wrote the beforementioned module to
> reproduce the race and make sure that this is no driver issue.
>
> With this module the warning could be triggered after a few cycles.
> With the patch applied, I did not see the warning again even after
> > 10.000 cycles.

Ok, fair enough. Care to resend the patch again so I can review it once
more?

thanks,

greg k-h
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When a device is registered to a bus it will be a) added to the list
of devices of the bus and b) bind to a driver (if one matches). As a
result of a driver being registered at this bus between a) and b) this
device could already be bound to a driver. This leads to a warning
and incorrect refcounting.
To fix this add a check to device_attach to identify an already bound
device.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
---
drivers/base/dd.c | 5 +++++
1 file changed, 5 insertions(+)

--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -245,6 +245,10 @@ int device_attach(struct device *dev)

device_lock(dev);
if (dev->driver) {
+ if (klist_node_attached(&dev->p->knode_driver)) {
+ ret = 1;
+ goto out_unlock;
+ }
ret = device_bind_driver(dev);
if (ret == 0)
ret = 1;
@@ -257,6 +261,7 @@ int device_attach(struct device *dev)
ret = bus_for_each_drv(dev->bus, NULL, dev, __device_attach);
pm_runtime_put_sync(dev);
}
+out_unlock:
device_unlock(dev);
return ret;
}
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On Tue, Apr 12, 2011 at 07:05:37PM +0200, Sebastian Ott wrote:
>
> When a device is registered to a bus it will be a) added to the list
> of devices of the bus and b) bind to a driver (if one matches). As a
> result of a driver being registered at this bus between a) and b) this
> device could already be bound to a driver. This leads to a warning
> and incorrect refcounting.
> To fix this add a check to device_attach to identify an already bound
> device.
>
> Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>

Thanks, I'll queue this up for .40.

greg k-h
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