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IB/usnic: Fix potential deadlock

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Acquiring the rtnl lock while holding usdev_lock could result in a
deadlock.

For example:

usnic_ib_query_port()
| mutex_lock(&us_ibdev->usdev_lock)
 | ib_get_eth_speed()
  | rtnl_lock()

rtnl_lock()
| usnic_ib_netdevice_event()
 | mutex_lock(&us_ibdev->usdev_lock)

This commit moves the usdev_lock acquisition after the rtnl lock has been
released.

This is safe to do because usdev_lock is not protecting anything being
accessed in ib_get_eth_speed(). Hence, the correct order of holding locks
(rtnl -> usdev_lock) is not violated.

Signed-off-by: Parvi Kaustubhi <pkaustub@cisco.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
This commit is contained in:
Parvi Kaustubhi 2018-12-11 14:15:42 -08:00 committed by Jason Gunthorpe
parent 50c582de1d
commit 8036e90f92
1 changed files with 7 additions and 4 deletions
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11
drivers/infiniband/hw/usnic/usnic_ib_verbs.c
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@ -336,13 +336,16 @@ int usnic_ib_query_port(struct ib_device *ibdev, u8 port,
usnic_dbg("\n");
mutex_lock(&us_ibdev->usdev_lock);
if (ib_get_eth_speed(ibdev, port, &props->active_speed,
&props->active_width)) {
mutex_unlock(&us_ibdev->usdev_lock);
&props->active_width))
return -EINVAL;
}
/*
* usdev_lock is acquired after (and not before) ib_get_eth_speed call
* because acquiring rtnl_lock in ib_get_eth_speed, while holding
* usdev_lock could lead to a deadlock.
*/
mutex_lock(&us_ibdev->usdev_lock);
/* props being zeroed by the caller, avoid zeroing it here */
props->lid = 0;