[PATCH 4.9 047/139] net: enic: Cure the enic api locking trainwreck

Greg Kroah-Hartman
2020-10-27T18:19:29Z

From: Thomas Gleixner <tglx@linutronix.de>

[ Upstream commit a53b59ece86c86d16d12ccdaa1ad0c78250a9d96 ]

enic_dev_wait() has a BUG_ON(in_interrupt()).

Chasing the callers of enic_dev_wait() revealed the gems of enic_reset()
and enic_tx_hang_reset() which are both invoked through work queues in
order to be able to call rtnl_lock(). So far so good.

After locking rtnl both functions acquire enic::enic_api_lock which
serializes against the (ab)use from infiniband. This is where the
trainwreck starts.

enic::enic_api_lock is a spin_lock() which implicitly disables preemption,
but both functions invoke a ton of functions under that lock which can
sleep. The BUG_ON(in_interrupt()) does not trigger in that case because it
can't detect the preempt disabled condition.

This clearly has never been tested with any of the mandatory debug options
for 7+ years, which would have caught that for sure.

Cure it by adding a enic_api_busy member to struct enic, which is modified
and evaluated with enic::enic_api_lock held.

If enic_api_devcmd_proxy_by_index() observes enic::enic_api_busy as true,
it drops enic::enic_api_lock and busy waits for enic::enic_api_busy to
become false.

It would be smarter to wait for a completion of that busy period, but
enic_api_devcmd_proxy_by_index() is called with other spin locks held which
obviously can't sleep.

Remove the BUG_ON(in_interrupt()) check as well because it's incomplete and
with proper debugging enabled the problem would have been caught from the
debug checks in schedule_timeout().

Fixes: 0b038566c0ea ("drivers/net: enic: Add an interface for USNIC to interact with firmware")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/ethernet/cisco/enic/enic.h | 1 +
drivers/net/ethernet/cisco/enic/enic_api.c | 6 +++++
drivers/net/ethernet/cisco/enic/enic_main.c | 27 ++++++++++++++++-----
3 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/cisco/enic/enic.h b/drivers/net/ethernet/cisco/enic/enic.h
index 130f910e47854..b6ebcee40a0d4 100644
--- a/drivers/net/ethernet/cisco/enic/enic.h
+++ b/drivers/net/ethernet/cisco/enic/enic.h
@@ -163,6 +163,7 @@ struct enic {
u16 num_vfs;
#endif
spinlock_t enic_api_lock;
+ bool enic_api_busy;
struct enic_port_profile *pp;

/* work queue cache line section */
diff --git a/drivers/net/ethernet/cisco/enic/enic_api.c b/drivers/net/ethernet/cisco/enic/enic_api.c
index b161f24522b87..b028ea2dec2b9 100644
--- a/drivers/net/ethernet/cisco/enic/enic_api.c
+++ b/drivers/net/ethernet/cisco/enic/enic_api.c
@@ -34,6 +34,12 @@ int enic_api_devcmd_proxy_by_index(struct net_device *netdev, int vf,
struct vnic_dev *vdev = enic->vdev;

spin_lock(&enic->enic_api_lock);
+ while (enic->enic_api_busy) {
+ spin_unlock(&enic->enic_api_lock);
+ cpu_relax();
+ spin_lock(&enic->enic_api_lock);
+ }
+
spin_lock_bh(&enic->devcmd_lock);

vnic_dev_cmd_proxy_by_index_start(vdev, vf);
diff --git a/drivers/net/ethernet/cisco/enic/enic_main.c b/drivers/net/ethernet/cisco/enic/enic_main.c
index 96290b83dfde9..3a3f3a7d7a75f 100644
--- a/drivers/net/ethernet/cisco/enic/enic_main.c
+++ b/drivers/net/ethernet/cisco/enic/enic_main.c
@@ -1938,8 +1938,6 @@ static int enic_dev_wait(struct vnic_dev *vdev,
int done;
int err;

- BUG_ON(in_interrupt());
-
err = start(vdev, arg);
if (err)
return err;
@@ -2116,6 +2114,13 @@ static int enic_set_rss_nic_cfg(struct enic *enic)
rss_hash_bits, rss_base_cpu, rss_enable);
}

+static void enic_set_api_busy(struct enic *enic, bool busy)
+{
+ spin_lock(&enic->enic_api_lock);
+ enic->enic_api_busy = busy;
+ spin_unlock(&enic->enic_api_lock);
+}
+
static void enic_reset(struct work_struct *work)
{
struct enic *enic = container_of(work, struct enic, reset);
@@ -2125,7 +2130,9 @@ static void enic_reset(struct work_struct *work)

rtnl_lock();

- spin_lock(&enic->enic_api_lock);
+ /* Stop any activity from infiniband */
+ enic_set_api_busy(enic, true);
+
enic_stop(enic->netdev);
enic_dev_soft_reset(enic);
enic_reset_addr_lists(enic);
@@ -2133,7 +2140,10 @@ static void enic_reset(struct work_struct *work)
enic_set_rss_nic_cfg(enic);
enic_dev_set_ig_vlan_rewrite_mode(enic);
enic_open(enic->netdev);
- spin_unlock(&enic->enic_api_lock);
+
+ /* Allow infiniband to fiddle with the device again */
+ enic_set_api_busy(enic, false);
+
call_netdevice_notifiers(NETDEV_REBOOT, enic->netdev);

rtnl_unlock();
@@ -2145,7 +2155,9 @@ static void enic_tx_hang_reset(struct work_struct *work)

rtnl_lock();

- spin_lock(&enic->enic_api_lock);
+ /* Stop any activity from infiniband */
+ enic_set_api_busy(enic, true);
+
enic_dev_hang_notify(enic);
enic_stop(enic->netdev);
enic_dev_hang_reset(enic);
@@ -2154,7 +2166,10 @@ static void enic_tx_hang_reset(struct work_struct *work)
enic_set_rss_nic_cfg(enic);
enic_dev_set_ig_vlan_rewrite_mode(enic);
enic_open(enic->netdev);
- spin_unlock(&enic->enic_api_lock);
+
+ /* Allow infiniband to fiddle with the device again */
+ enic_set_api_busy(enic, false);
+
call_netdevice_notifiers(NETDEV_REBOOT, enic->netdev);

rtnl_unlock();
--
2.25.1