From b93984c9afacd4fe32b785d52a93660d91202b10 Mon Sep 17 00:00:00 2001 From: David Daney Date: Wed, 4 Jul 2012 12:06:16 +0000 Subject: [PATCH] netdev/phy: Fixup lockdep warnings in mdio-mux.c 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: [] mdio_mux_read+0x38/0xa0 but task is already holding lock: (&bus->mdio_lock){+.+...}, at: [] 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 Signed-off-by: David S. Miller --- drivers/net/phy/mdio-mux.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/drivers/net/phy/mdio-mux.c b/drivers/net/phy/mdio-mux.c index 39ea0674dcd..5c120189ec8 100644 --- a/drivers/net/phy/mdio-mux.c +++ b/drivers/net/phy/mdio-mux.c @@ -46,7 +46,13 @@ static int mdio_mux_read(struct mii_bus *bus, int phy_id, int regnum) struct mdio_mux_parent_bus *pb = cb->parent; int r; - mutex_lock(&pb->mii_bus->mdio_lock); + /* In theory multiple mdio_mux could be stacked, thus creating + * more than a single level of nesting. But in practice, + * SINGLE_DEPTH_NESTING will cover the vast majority of use + * cases. We use it, instead of trying to handle the general + * case. + */ + mutex_lock_nested(&pb->mii_bus->mdio_lock, SINGLE_DEPTH_NESTING); r = pb->switch_fn(pb->current_child, cb->bus_number, pb->switch_data); if (r) goto out; @@ -71,7 +77,7 @@ static int mdio_mux_write(struct mii_bus *bus, int phy_id, int r; - mutex_lock(&pb->mii_bus->mdio_lock); + mutex_lock_nested(&pb->mii_bus->mdio_lock, SINGLE_DEPTH_NESTING); r = pb->switch_fn(pb->current_child, cb->bus_number, pb->switch_data); if (r) goto out; -- 2.20.1