From 7b738036bcfd3a84eca7e2587dd36ae0b6d12afa Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 29 Sep 2020 22:25:10 +0200
Subject: [PATCH 3/3] net: enic: Cure the enic api locking trainwreck
Git-commit: a53b59ece86c86d16d12ccdaa1ad0c78250a9d96
Patch-mainline: v5.10-rc1
References: git-fixes

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: Denis Kirjanov <denis.kirjanov@suse.com>
---
 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 0dd64acd2a3f..08cac1bfacaf 100644
--- a/drivers/net/ethernet/cisco/enic/enic.h
+++ b/drivers/net/ethernet/cisco/enic/enic.h
@@ -171,6 +171,7 @@ 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 b161f24522b8..b028ea2dec2b 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 212c9b6756a8..7f7f183b981e 100644
--- a/drivers/net/ethernet/cisco/enic/enic_main.c
+++ b/drivers/net/ethernet/cisco/enic/enic_main.c
@@ -2145,8 +2145,6 @@ 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;
@@ -2334,6 +2332,13 @@ 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);
@@ -2343,7 +2348,9 @@ 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);
@@ -2351,7 +2358,10 @@ 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();
@@ -2363,7 +2373,9 @@ 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);
@@ -2372,7 +2384,10 @@ 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();
-- 
2.16.4