sysfs: cannot create duplicate filename

[Sebastian Ott]

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@xxxxxxxxxxxxxxxxxx>
---
 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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