netdev - [PATCH net-next v2 5/7] ibmvnic: serialize access to work queue

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Date:   Tue, 12 Jan 2021 10:14:39 -0800
From:   Sukadev Bhattiprolu <sukadev@...ux.ibm.com>
To:     netdev@...r.kernel.org
Cc:     Dany Madden <drt@...ux.ibm.com>, Lijun Pan <ljp@...ux.ibm.com>,
        Rick Lindsley <ricklind@...ux.ibm.com>, sukadev@...ux.ibm.com
Subject: [PATCH net-next v2 5/7] ibmvnic: serialize access to work queue

The work queue is used to queue reset requests like CHANGE-PARAM or
FAILOVER resets for the worker thread. When the adapter is being removed
the adapter state is set to VNIC_REMOVING and the work queue is flushed
so no new work is added. However the check for adapter being removed is
racy in that the adapter can go into REMOVING state just after we check
and we might end up adding work just as it is being flushed (or after).

Use a new spin lock, ->remove_lock to ensure that after (while) the work
queue is (being) flushed, no new work is queued.

A follow-on patch will convert the existing ->state_lock from a spin lock
to to a mutex to allow us to hold it for longer periods of time. Since
work can be scheduled from a tasklet, we cannot block on the mutex, so
use a new spin lock.

Fixes: 6954a9e4192b ("ibmvnic: Flush existing work items before device removal")
Signed-off-by: Sukadev Bhattiprolu <sukadev@...ux.ibm.com>
---
 drivers/net/ethernet/ibm/ibmvnic.c | 15 ++++++++++++++-
 drivers/net/ethernet/ibm/ibmvnic.h |  2 ++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
index ad551418ac63..7645df37e886 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -2435,6 +2435,7 @@ static int ibmvnic_reset(struct ibmvnic_adapter *adapter,
 			 enum ibmvnic_reset_reason reason)
 {
 	struct net_device *netdev = adapter->netdev;
+	unsigned long flags;
 	int ret;
 
 	if (adapter->state == VNIC_PROBING) {
@@ -2443,6 +2444,8 @@ static int ibmvnic_reset(struct ibmvnic_adapter *adapter,
 		goto err;
 	}
 
+	spin_lock_irqsave(&adapter->remove_lock, flags);
+
 	/*
 	 * If failover is pending don't schedule any other reset.
 	 * Instead let the failover complete. If there is already a
@@ -2465,8 +2468,9 @@ static int ibmvnic_reset(struct ibmvnic_adapter *adapter,
 	netdev_dbg(adapter->netdev, "Scheduling reset (reason %d)\n", reason);
 	schedule_work(&adapter->ibmvnic_reset);
 
-	return 0;
+	ret = 0;
 err:
+	spin_unlock_irqrestore(&adapter->remove_lock, flags);
 	return -ret;
 }
 
@@ -5387,6 +5391,7 @@ static int ibmvnic_probe(struct vio_dev *dev, const struct vio_device_id *id)
 	memset(&adapter->pending_resets, 0, sizeof(adapter->pending_resets));
 	spin_lock_init(&adapter->rwi_lock);
 	spin_lock_init(&adapter->state_lock);
+	spin_lock_init(&adapter->remove_lock);
 	mutex_init(&adapter->fw_lock);
 	init_completion(&adapter->init_done);
 	init_completion(&adapter->fw_done);
@@ -5467,7 +5472,15 @@ static int ibmvnic_remove(struct vio_dev *dev)
 		return -EBUSY;
 	}
 
+	/* If ibmvnic_reset() is scheduling a reset, wait for it to
+	 * finish. Then prevent it from scheduling any more resets
+	 * and have the reset functions ignore any resets that have
+	 * already been scheduled.
+	 */
+	spin_lock_irqsave(&adapter->remove_lock, flags);
 	adapter->state = VNIC_REMOVING;
+	spin_unlock_irqrestore(&adapter->remove_lock, flags);
+
 	spin_unlock_irqrestore(&adapter->state_lock, flags);
 
 	flush_work(&adapter->ibmvnic_reset);
diff --git a/drivers/net/ethernet/ibm/ibmvnic.h b/drivers/net/ethernet/ibm/ibmvnic.h
index 1179a95a3f92..2779696ade09 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.h
+++ b/drivers/net/ethernet/ibm/ibmvnic.h
@@ -1081,6 +1081,8 @@ struct ibmvnic_adapter {
 	spinlock_t rwi_lock;
 	enum ibmvnic_reset_reason pending_resets[VNIC_RESET_MAX-1];
 	short next_reset;
+	/* serialize ibmvnic_reset() and ibmvnic_remove() */
+	spinlock_t remove_lock;
 	struct work_struct ibmvnic_reset;
 	struct delayed_work ibmvnic_delayed_reset;
 	unsigned long resetting;
-- 
2.26.2