With lockdep enabled we get:
=============================================
[ INFO: possible recursive locking detected ]
3.4.4-Cavium-Octeon+ #313 Not tainted
---------------------------------------------
kworker/u:1/36 is trying to acquire lock:
(&bus->mdio_lock){+.+...}, at: [<ffffffff813da7e8>] mdio_mux_read+0x38/0xa0
but task is already holding lock:
(&bus->mdio_lock){+.+...}, at: [<ffffffff813d79e4>] mdiobus_read+0x44/0x88
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&bus->mdio_lock);
lock(&bus->mdio_lock);
*** DEADLOCK ***
May be due to missing lock nesting notation
.
.
.
This is a false positive, since we are indeed using 'nested' locking,
we need to use mutex_lock_nested().
Now in theory we can stack multiple MDIO multiplexers, but that would
require passing the nesting level (which is difficult to know) to
mutex_lock_nested(). Instead we assume the simple case of a single
level of nesting. Since these are only warning messages, it isn't so
important to solve the general case.
Signed-off-by: David Daney <david.daney@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
b93984c9af