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    Subject[PATCH 4.9 094/171] IB/ipoib: Fix lockdep issue found on ipoib_ib_dev_heavy_flush
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    [ Upstream commit 1f80bd6a6cc8358b81194e1f5fc16449947396ec ]

    The locking order of vlan_rwsem (LOCK A) and then rtnl (LOCK B),
    contradicts other flows such as ipoib_open possibly causing a deadlock.
    To prevent this deadlock heavy flush is called with RTNL locked and
    only then tries to acquire vlan_rwsem.
    This deadlock is possible only when there are child interfaces.

    [ 140.941758] ======================================================
    [ 140.946276] WARNING: possible circular locking dependency detected
    [ 140.950950] 4.15.0-rc1+ #9 Tainted: G O
    [ 140.954797] ------------------------------------------------------
    [ 140.959424] kworker/u32:1/146 is trying to acquire lock:
    [ 140.963450] (rtnl_mutex){+.+.}, at: [<ffffffffc083516a>] __ipoib_ib_dev_flush+0x2da/0x4e0 [ib_ipoib]
    [ 140.970006]
    but task is already holding lock:
    [ 140.975141] (&priv->vlan_rwsem){++++}, at: [<ffffffffc0834ee1>] __ipoib_ib_dev_flush+0x51/0x4e0 [ib_ipoib]
    [ 140.982105]
    which lock already depends on the new lock.
    [ 140.990023]
    the existing dependency chain (in reverse order) is:
    [ 140.998650]
    -> #1 (&priv->vlan_rwsem){++++}:
    [ 141.005276] down_read+0x4d/0xb0
    [ 141.009560] ipoib_open+0xad/0x120 [ib_ipoib]
    [ 141.014400] __dev_open+0xcb/0x140
    [ 141.017919] __dev_change_flags+0x1a4/0x1e0
    [ 141.022133] dev_change_flags+0x23/0x60
    [ 141.025695] devinet_ioctl+0x704/0x7d0
    [ 141.029156] sock_do_ioctl+0x20/0x50
    [ 141.032526] sock_ioctl+0x221/0x300
    [ 141.036079] do_vfs_ioctl+0xa6/0x6d0
    [ 141.039656] SyS_ioctl+0x74/0x80
    [ 141.042811] entry_SYSCALL_64_fastpath+0x1f/0x96
    [ 141.046891]
    -> #0 (rtnl_mutex){+.+.}:
    [ 141.051701] lock_acquire+0xd4/0x220
    [ 141.055212] __mutex_lock+0x88/0x970
    [ 141.058631] __ipoib_ib_dev_flush+0x2da/0x4e0 [ib_ipoib]
    [ 141.063160] __ipoib_ib_dev_flush+0x71/0x4e0 [ib_ipoib]
    [ 141.067648] process_one_work+0x1f5/0x610
    [ 141.071429] worker_thread+0x4a/0x3f0
    [ 141.074890] kthread+0x141/0x180
    [ 141.078085] ret_from_fork+0x24/0x30
    [ 141.081559]

    other info that might help us debug this:
    [ 141.088967] Possible unsafe locking scenario:
    [ 141.094280] CPU0 CPU1
    [ 141.097953] ---- ----
    [ 141.101640] lock(&priv->vlan_rwsem);
    [ 141.104771] lock(rtnl_mutex);
    [ 141.109207] lock(&priv->vlan_rwsem);
    [ 141.114032] lock(rtnl_mutex);
    [ 141.116800]
    *** DEADLOCK ***

    Fixes: b4b678b06f6e ("IB/ipoib: Grab rtnl lock on heavy flush when calling ndo_open/stop")
    Signed-off-by: Alex Vesker <valex@mellanox.com>
    Signed-off-by: Leon Romanovsky <leon@kernel.org>
    Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/infiniband/ulp/ipoib/ipoib_ib.c | 7 +++----
    1 file changed, 3 insertions(+), 4 deletions(-)

    diff --git a/drivers/infiniband/ulp/ipoib/ipoib_ib.c b/drivers/infiniband/ulp/ipoib/ipoib_ib.c
    index 34122c96522b..3dd5bf6c6c7a 100644
    --- a/drivers/infiniband/ulp/ipoib/ipoib_ib.c
    +++ b/drivers/infiniband/ulp/ipoib/ipoib_ib.c
    @@ -1190,13 +1190,10 @@ static void __ipoib_ib_dev_flush(struct ipoib_dev_priv *priv,
    ipoib_ib_dev_down(dev);

    if (level == IPOIB_FLUSH_HEAVY) {
    - rtnl_lock();
    if (test_bit(IPOIB_FLAG_INITIALIZED, &priv->flags))
    ipoib_ib_dev_stop(dev);

    - result = ipoib_ib_dev_open(dev);
    - rtnl_unlock();
    - if (result)
    + if (ipoib_ib_dev_open(dev))
    return;

    if (netif_queue_stopped(dev))
    @@ -1236,7 +1233,9 @@ void ipoib_ib_dev_flush_heavy(struct work_struct *work)
    struct ipoib_dev_priv *priv =
    container_of(work, struct ipoib_dev_priv, flush_heavy);

    + rtnl_lock();
    __ipoib_ib_dev_flush(priv, IPOIB_FLUSH_HEAVY, 0);
    + rtnl_unlock();
    }

    void ipoib_ib_dev_cleanup(struct net_device *dev)
    --
    2.17.1


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