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authorDavid Daney <david.daney@cavium.com>2012-07-04 12:06:16 +0000
committerDavid S. Miller <davem@davemloft.net>2012-07-09 00:12:42 -0700
commitb93984c9afacd4fe32b785d52a93660d91202b10 (patch)
treebb140d9abc23831e0771940febdd4392aeffe689 /drivers/net/phy/mdio-mux.c
parentd4e41649434cd6db2e69783130cba81886dac97f (diff)
downloadblackbird-op-linux-b93984c9afacd4fe32b785d52a93660d91202b10.tar.gz
blackbird-op-linux-b93984c9afacd4fe32b785d52a93660d91202b10.zip
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: [<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>
Diffstat (limited to 'drivers/net/phy/mdio-mux.c')
-rw-r--r--drivers/net/phy/mdio-mux.c10
1 files changed, 8 insertions, 2 deletions
diff --git a/drivers/net/phy/mdio-mux.c b/drivers/net/phy/mdio-mux.c
index 39ea0674dcde..5c120189ec86 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;
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