Currently rtnl mutex is grabbed during fcoe create, destroy, enable
and disable operations while sysfs s_active read mutex is already
held, but simultaneously other networking events could try grabbing
write s_active mutex while rtnl is already held and that is causing
circular lock warning, its detailed log pasted at end.

In this log, the rtnl was held before write s_active during device
renaming but there are more such cases as Joe reported another
instance with tg3 open at:-
http://www.open-fcoe.org/pipermail/devel/2010-February/008263.html

This patch fixes this issue by not waiting for rtnl mutex during
fcoe ops, that means if rtnl mutex is not immediately available
then restart_syscall() to allow others waiting in line to
grab s_active along with rtnl mutex to finish their work first
under these mutex.

Currently rtnl mutex was grabbed twice during fcoe_destroy call flow,
second grab was from fcoe_if_destroy called from fcoe_destroy after
dropping rtnl mutex before calling fcoe_if_destroy, so instead made
fcoe_if_destroy always called with rtnl mutex held to have this mutex
grabbed only once in this code path.

However left matching rtnl_unlock as-is in its original place as it was
dropped there for good reason since very next call causes synchronous
fip worker flush and if rtnl mutex is still held before flush
then that would cause new circular warning between fip->recv_work and
rtnl mutex, I've added detailed comment for this on fcoe_if_destroy
calling and rtnl muxtes unlocking.

=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.33.1linux-stable-2.6.33 #1
-------------------------------------------------------
fcoemon/18823 is trying to acquire lock:
(fcoe_config_mutex){+.+.+.}, at: [<ffffffffa02ba5fc>] fcoe_create+0x27/0x4f7
[fcoe]

but task is already holding lock:
(s_active){++++.+}, at: [<ffffffff8115ef93>] sysfs_get_active_two+0x31/0x48

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (s_active){++++.+}:
   [<ffffffff81077bdb>] __lock_acquire+0xb73/0xd2b
   [<ffffffff81077e60>] lock_acquire+0xcd/0xf1
   [<ffffffff8115e5df>] sysfs_deactivate+0x8b/0xe0
   [<ffffffff8115edfb>] sysfs_addrm_finish+0x36/0x55
   [<ffffffff8115d0cc>] sysfs_hash_and_remove+0x53/0x6a
   [<ffffffff8115f353>] sysfs_remove_link+0x21/0x23
   [<ffffffff812b6c93>] device_rename+0x99/0xcb
   [<ffffffff8138dbf0>] dev_change_name+0xd5/0x1d2
   [<ffffffff8138deee>] dev_ifsioc+0x201/0x2ac
   [<ffffffff8138e4ba>] dev_ioctl+0x521/0x632
   [<ffffffff81379e43>] sock_do_ioctl+0x3d/0x47
   [<ffffffff8137a254>] sock_ioctl+0x213/0x222
   [<ffffffff81114614>] vfs_ioctl+0x32/0xa6
   [<ffffffff81114b94>] do_vfs_ioctl+0x490/0x4d6
   [<ffffffff81114c30>] sys_ioctl+0x56/0x79
   [<ffffffff81009b42>] system_call_fastpath+0x16/0x1b

-> #1 (rtnl_mutex){+.+.+.}:
   [<ffffffff81077bdb>] __lock_acquire+0xb73/0xd2b
   [<ffffffff81077e60>] lock_acquire+0xcd/0xf1
   [<ffffffff8142f343>] __mutex_lock_common+0x4b/0x383
   [<ffffffff8142f73f>] mutex_lock_nested+0x3e/0x43
   [<ffffffff813959f9>] rtnl_lock+0x17/0x19
   [<ffffffff8138ccae>] register_netdevice_notifier+0x1e/0x19b
   [<ffffffffa02580c1>] 0xffffffffa02580c1
   [<ffffffff81002069>] do_one_initcall+0x5e/0x15e
   [<ffffffff81084094>] sys_init_module+0xd8/0x23a
   [<ffffffff81009b42>] system_call_fastpath+0x16/0x1b

-> #0 (fcoe_config_mutex){+.+.+.}:
   [<ffffffff81077a85>] __lock_acquire+0xa1d/0xd2b
   [<ffffffff81077e60>] lock_acquire+0xcd/0xf1
   [<ffffffff8142f343>] __mutex_lock_common+0x4b/0x383
   [<ffffffff8142f73f>] mutex_lock_nested+0x3e/0x43
   [<ffffffffa02ba5fc>] fcoe_create+0x27/0x4f7 [fcoe]
   [<ffffffff810635b1>] param_attr_store+0x27/0x35
   [<ffffffff81063619>] module_attr_store+0x26/0x2a
   [<ffffffff8115dae3>] sysfs_write_file+0x108/0x144
   [<ffffffff81107bd1>] vfs_write+0xae/0x10b
   [<ffffffff81107cee>] sys_write+0x4a/0x6e
   [<ffffffff81009b42>] system_call_fastpath+0x16/0x1b

other info that might help us debug this:

3 locks held by fcoemon/18823:
#0:  (&buffer->mutex){+.+.+.}, at: [<ffffffff8115da17>]
sysfs_write_file+0x3c/0x144
#1:  (s_active){++++.+}, at: [<ffffffff8115ef86>]
sysfs_get_active_two+0x24/0x48
#2:  (s_active){++++.+}, at: [<ffffffff8115ef93>]
sysfs_get_active_two+0x31/0x48

stack backtrace:
Pid: 18823, comm: fcoemon Tainted: G        W  2.6.33.1linux-stable-2.6.33 #1
Call Trace:
[<ffffffff81076c38>] print_circular_bug+0xa8/0xb6
[<ffffffff81077a85>] __lock_acquire+0xa1d/0xd2b
[<ffffffffa02ba5fc>] ? fcoe_create+0x27/0x4f7 [fcoe]
[<ffffffff81077e60>] lock_acquire+0xcd/0xf1
[<ffffffffa02ba5fc>] ? fcoe_create+0x27/0x4f7 [fcoe]
[<ffffffffa02ba5fc>] ? fcoe_create+0x27/0x4f7 [fcoe]
[<ffffffff8142f343>] __mutex_lock_common+0x4b/0x383
[<ffffffffa02ba5fc>] ? fcoe_create+0x27/0x4f7 [fcoe]
[<ffffffff8106ac70>] ? cpu_clock+0x43/0x5e
[<ffffffff81074e12>] ? lockstat_clock+0x11/0x13
[<ffffffff81074e40>] ? lock_release_holdtime+0x2c/0x127
[<ffffffff8115ef93>] ? sysfs_get_active_two+0x31/0x48
[<ffffffff8142f73f>] mutex_lock_nested+0x3e/0x43
[<ffffffffa02ba5fc>] fcoe_create+0x27/0x4f7 [fcoe]
[<ffffffff810635b1>] param_attr_store+0x27/0x35
[<ffffffff81063619>] module_attr_store+0x26/0x2a
[<ffffffff8115dae3>] sysfs_write_file+0x108/0x144
[<ffffffff81107bd1>] vfs_write+0xae/0x10b
[<ffffffff81076596>] ? trace_hardirqs_on_caller+0x125/0x150
[<ffffffff81107cee>] sys_write+0x4a/0x6e
[<ffffffff81009b42>] system_call_fastpath+0x16/0x1b
Signed-off-by: NVasu Dev <vasu.dev@intel.com>
Signed-off-by: NRobert Love <robert.w.love@intel.com>
Signed-off-by: NJames Bottomley <James.Bottomley@suse.de>