netdev - [PATCH net 1/1] ibmvnic: serialize access to work queue on remove

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Date:   Fri, 12 Feb 2021 20:42:50 -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>, uwe@...ine-koenig.org,
        saeed@...nel.org, sukadev@...ux.ibm.com
Subject: [PATCH net 1/1] ibmvnic: serialize access to work queue on remove

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).

The ->rwi_lock is already being used to serialize queue/dequeue work.
Extend its usage ensure there is no race when scheduling/flushing work.

Fixes: 6954a9e4192b ("ibmvnic: Flush existing work items before device removal")
Signed-off-by: Sukadev Bhattiprolu <sukadev@...ux.ibm.com>
Cc:Uwe Kleine-König <uwe@...ine-koenig.org>
Cc:Saeed Mahameed <saeed@...nel.org>
---
Changelog
	An earlier version was reviewed by Saeed Mahmeed. But I have deferred
	some earlier patches in that set. Also, now extend the use of ->rwi_lock
	rather than defining a new lock.
---
 drivers/net/ethernet/ibm/ibmvnic.c | 27 ++++++++++++++++++++-------
 drivers/net/ethernet/ibm/ibmvnic.h |  5 ++++-
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
index ce6b1cb0b0f9..004565b18a03 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -2442,6 +2442,8 @@ static int ibmvnic_reset(struct ibmvnic_adapter *adapter,
 	unsigned long flags;
 	int ret;
 
+	spin_lock_irqsave(&adapter->rwi_lock, flags);
+
 	/*
 	 * If failover is pending don't schedule any other reset.
 	 * Instead let the failover complete. If there is already a
@@ -2462,14 +2464,11 @@ static int ibmvnic_reset(struct ibmvnic_adapter *adapter,
 		goto err;
 	}
 
-	spin_lock_irqsave(&adapter->rwi_lock, flags);
-
 	list_for_each(entry, &adapter->rwi_list) {
 		tmp = list_entry(entry, struct ibmvnic_rwi, list);
 		if (tmp->reset_reason == reason) {
 			netdev_dbg(netdev, "Skipping matching reset, reason=%d\n",
 				   reason);
-			spin_unlock_irqrestore(&adapter->rwi_lock, flags);
 			ret = EBUSY;
 			goto err;
 		}
@@ -2477,8 +2476,6 @@ static int ibmvnic_reset(struct ibmvnic_adapter *adapter,
 
 	rwi = kzalloc(sizeof(*rwi), GFP_ATOMIC);
 	if (!rwi) {
-		spin_unlock_irqrestore(&adapter->rwi_lock, flags);
-		ibmvnic_close(netdev);
 		ret = ENOMEM;
 		goto err;
 	}
@@ -2491,12 +2488,17 @@ static int ibmvnic_reset(struct ibmvnic_adapter *adapter,
 	}
 	rwi->reset_reason = reason;
 	list_add_tail(&rwi->list, &adapter->rwi_list);
-	spin_unlock_irqrestore(&adapter->rwi_lock, flags);
 	netdev_dbg(adapter->netdev, "Scheduling reset (reason %d)\n", reason);
 	schedule_work(&adapter->ibmvnic_reset);
 
-	return 0;
+	ret = 0;
 err:
+	/* ibmvnic_close() below can block, so drop the lock first */
+	spin_unlock_irqrestore(&adapter->rwi_lock, flags);
+
+	if (ret == ENOMEM)
+		ibmvnic_close(netdev);
+
 	return -ret;
 }
 
@@ -5512,7 +5514,18 @@ static int ibmvnic_remove(struct vio_dev *dev)
 	unsigned long flags;
 
 	spin_lock_irqsave(&adapter->state_lock, flags);
+
+	/* If ibmvnic_reset() is scheduling a reset, wait for it to
+	 * finish. Then, set the state to REMOVING to prevent it from
+	 * scheduling any more work and to have reset functions ignore
+	 * any resets that have already been scheduled. Drop the lock
+	 * after setting state, so __ibmvnic_reset() which is called
+	 * from the flush_work() below, can make progress.
+	 */
+	spin_lock_irqsave(&adapter->rwi_lock, flags);
 	adapter->state = VNIC_REMOVING;
+	spin_unlock_irqrestore(&adapter->rwi_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 c09c3f6bba9f..3cccbba70365 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.h
+++ b/drivers/net/ethernet/ibm/ibmvnic.h
@@ -1081,6 +1081,7 @@ struct ibmvnic_adapter {
 	struct tasklet_struct tasklet;
 	enum vnic_state state;
 	enum ibmvnic_reset_reason reset_reason;
+	/* when taking both state and rwi locks, take state lock first */
 	spinlock_t rwi_lock;
 	struct list_head rwi_list;
 	struct work_struct ibmvnic_reset;
@@ -1097,6 +1098,8 @@ struct ibmvnic_adapter {
 	struct ibmvnic_tunables desired;
 	struct ibmvnic_tunables fallback;
 
-	/* Used for serializatin of state field */
+	/* Used for serialization of state field. When taking both state
+	 * and rwi locks, take state lock first.
+	 */
 	spinlock_t state_lock;
 };
-- 
2.26.2