[PATCH] i2c: suppress lockdep warning on delete_device

[Alexander Sverdlin <alexander.sverdlin-OYasijW0DpE@public.gmane.org>]

i2c: suppress lockdep warning on delete_device

Since commit 846f99749ab68bbc7f75c74fec305de675b1a1bf the following lockdep
warning is thrown in case i2c device is removed (via delete_device sysfs
attribute) which contains subdevices (e.g. i2c multiplexer):

=============================================
[ INFO: possible recursive locking detected ]
3.8.7-0-sampleversion-fct #8 Tainted: G           O
---------------------------------------------
bash/3743 is trying to acquire lock:
  (s_active#110){++++.+}, at: [<ffffffff802b3048>] sysfs_hash_and_remove+0x58/0xc8

but task is already holding lock:
  (s_active#110){++++.+}, at: [<ffffffff802b3cb8>] sysfs_write_file+0xc8/0x208

other info that might help us debug this:
  Possible unsafe locking scenario:

        CPU0
        ----
   lock(s_active#110);
   lock(s_active#110);

  *** DEADLOCK ***

  May be due to missing lock nesting notation

4 locks held by bash/3743:
  #0:  (&buffer->mutex){+.+.+.}, at: [<ffffffff802b3c3c>] sysfs_write_file+0x4c/0x208
  #1:  (s_active#110){++++.+}, at: [<ffffffff802b3cb8>] sysfs_write_file+0xc8/0x208
  #2:  (&adap->userspace_clients_lock/1){+.+.+.}, at: [<ffffffff80454a18>] i2c_sysfs_delete_device+0x90/0x238
  #3:  (&__lockdep_no_validate__){......}, at: [<ffffffff803dcc24>] device_release_driver+0x24/0x48

stack backtrace:
Call Trace:
[<ffffffff80575cc8>] dump_stack+0x8/0x34
[<ffffffff801b50fc>] __lock_acquire+0x161c/0x2110
[<ffffffff801b5c3c>] lock_acquire+0x4c/0x70
[<ffffffff802b60cc>] sysfs_addrm_finish+0x19c/0x1e0
[<ffffffff802b3048>] sysfs_hash_and_remove+0x58/0xc8
[<ffffffff802b7d8c>] sysfs_remove_group+0x64/0x148
[<ffffffff803d990c>] device_remove_attrs+0x9c/0x1a8
[<ffffffff803d9b1c>] device_del+0x104/0x1d8
[<ffffffff803d9c18>] device_unregister+0x28/0x70
[<ffffffff8045505c>] i2c_del_adapter+0x1cc/0x328
[<ffffffff8045802c>] i2c_del_mux_adapter+0x14/0x38
[<ffffffffc025c108>] pca954x_remove+0x90/0xe0 [pca954x]
[<ffffffff804542f8>] i2c_device_remove+0x80/0xe8
[<ffffffff803dca9c>] __device_release_driver+0x74/0xf8
[<ffffffff803dcc2c>] device_release_driver+0x2c/0x48
[<ffffffff803dbc14>] bus_remove_device+0x13c/0x1d8
[<ffffffff803d9b24>] device_del+0x10c/0x1d8
[<ffffffff803d9c18>] device_unregister+0x28/0x70
[<ffffffff80454b08>] i2c_sysfs_delete_device+0x180/0x238
[<ffffffff802b3cd4>] sysfs_write_file+0xe4/0x208
[<ffffffff8023ddc4>] vfs_write+0xbc/0x160
[<ffffffff8023df6c>] SyS_write+0x54/0xd8
[<ffffffff8013d424>] handle_sys64+0x44/0x64

The problem is already known for USB and PCI subsystems. The reason is that
delete_device attribute is defined statically in i2c-core.c and used for all
devices in i2c subsystem.

Discussion of original USB problem:
http://lkml.indiana.edu/hypermail/linux/kernel/1204.3/01160.html

Commit 356c05d58af05d582e634b54b40050c73609617b introduced new macro to suppress
lockdep warnings for this special case and included workaround for USB code.

LKML discussion of the workaround:
http://lkml.indiana.edu/hypermail/linux/kernel/1205.1/03634.html

As i2c case is in principle the same, the same workaround could be used here.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin-OYasijW0DpE@public.gmane.org>
Cc: Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
Cc: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: Alan Stern <stern-nwvwT67g6+6dFdvTe/nMLpVzexx5G7lz@public.gmane.org>
Cc: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
Cc: Greg Kroah-Hartman <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>
---

--- linux-next.orig/drivers/i2c/i2c-core.c
+++ linux-next/drivers/i2c/i2c-core.c
@@ -892,7 +892,8 @@ i2c_sysfs_delete_device(struct device *d
  }

  static DEVICE_ATTR(new_device, S_IWUSR, NULL, i2c_sysfs_new_device);
-static DEVICE_ATTR(delete_device, S_IWUSR, NULL, i2c_sysfs_delete_device);
+static DEVICE_ATTR_IGNORE_LOCKDEP(delete_device, S_IWUSR, NULL,
+                                  i2c_sysfs_delete_device);

  static struct attribute *i2c_adapter_attrs[] = {
  	&dev_attr_name.attr,