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Message-ID: <1bd774566df5d634d58d49a064e5ca34@imap.linux.ibm.com>
Date: Sat, 13 Feb 2021 08:17:05 -0800
From: Dany Madden <drt@...ux.ibm.com>
To: Sukadev Bhattiprolu <sukadev@...ux.ibm.com>
Cc: netdev@...r.kernel.org, Lijun Pan <ljp@...ux.ibm.com>,
Rick Lindsley <ricklind@...ux.ibm.com>, uwe@...ine-koenig.org,
saeed@...nel.org
Subject: Re: [PATCH net 1/1] ibmvnic: serialize access to work queue on remove
On 2021-02-12 20:42, Sukadev Bhattiprolu wrote:
> 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>
Reviewed-by: Dany Madden <drt@...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;
> };
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