Re: [PATCH v2] IB/ipoib: fix for rare multicast join race condition.

[Leon Romanovsky <leon-2ukJVAZIZ/Y@public.gmane.org>]

A number of very minor comments:
1. Please remove dot at the end of commit message title.

On Sat, Feb 06, 2016 at 08:50:41AM -0500, Alex Estrin wrote:
> A narrow window for race condition still exist between
> multicast join thread and *dev_flush workers.
> A kernel crash caused by prolong erratic link state changes
> was observed (most likely a faulty cabling):
> 
> [167275.656270] BUG: unable to handle kernel NULL pointer dereference at
> 0000000000000020
> [167275.665973] IP: [<ffffffffa05f8f2e>] ipoib_mcast_join+0xae/0x1d0 [ib_ipoib]
> [167275.674443] PGD 0
> [167275.677373] Oops: 0000 [#1] SMP
> ...
> [167275.977530] Call Trace:
> [167275.982225]  [<ffffffffa05f92f0>] ? ipoib_mcast_free+0x200/0x200 [ib_ipoib]
> [167275.992024]  [<ffffffffa05fa1b7>] ipoib_mcast_join_task+0x2a7/0x490
> [ib_ipoib]
> [167276.002149]  [<ffffffff8109d5fb>] process_one_work+0x17b/0x470
> [167276.010754]  [<ffffffff8109e3cb>] worker_thread+0x11b/0x400
> [167276.019088]  [<ffffffff8109e2b0>] ? rescuer_thread+0x400/0x400
> [167276.027737]  [<ffffffff810a5aef>] kthread+0xcf/0xe0
> Here was a hit spot:
> ipoib_mcast_join() {
> ..............
>       rec.qkey      = priv->broadcast->mcmember.qkey;
>                                        ^^^^^^^
> .....
>  }
> Proposed patch should prevent multicast join task to continue
> if link state change is detected.
> 
> Signed-off-by: Alex Estrin <alex.estrin-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> ---
> 
> Changes from v1:
> No need to lock again if error detected.
> ---
>  drivers/infiniband/ulp/ipoib/ipoib_multicast.c |   14 ++++++++++++--
>  1 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
> index 050dfa1..3ce2f0a 100644
> --- a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
> +++ b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c
> @@ -456,7 +456,7 @@ out_locked:
>  	return status;
>  }
>  
> -static void ipoib_mcast_join(struct net_device *dev, struct ipoib_mcast *mcast)
> +static int ipoib_mcast_join(struct net_device *dev, struct ipoib_mcast *mcast)
>  {
>  	struct ipoib_dev_priv *priv = netdev_priv(dev);
>  	struct ib_sa_multicast *multicast;
> @@ -466,6 +466,9 @@ static void ipoib_mcast_join(struct net_device *dev, struct ipoib_mcast *mcast)
>  	ib_sa_comp_mask comp_mask;
>  	int ret = 0;
>  
> +	if (!priv->broadcast)
> +		return -EINVAL;
> +
>  	ipoib_dbg_mcast(priv, "joining MGID %pI6\n", mcast->mcmember.mgid.raw);
>  
>  	rec.mgid     = mcast->mcmember.mgid;
> @@ -539,6 +542,7 @@ static void ipoib_mcast_join(struct net_device *dev, struct ipoib_mcast *mcast)
>  		spin_unlock_irq(&priv->lock);
>  		complete(&mcast->done);
>  	}
> +	return 0;

2. This function declared as a void, it is an error to add "return 0".

>  }
>  
>  void ipoib_mcast_join_task(struct work_struct *work)
> @@ -611,6 +615,11 @@ void ipoib_mcast_join_task(struct work_struct *work)
>  	 * and attached
>  	 */
>  	list_for_each_entry(mcast, &priv->multicast_list, list) {
> +		if (!test_bit(IPOIB_FLAG_OPER_UP, &priv->flags)) {
> +			mcast = NULL;
> +			delay_until = 0;
> +			goto out;
> +		}
>  		if (IS_ERR_OR_NULL(mcast->mc) &&
>  		    !test_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags) &&
>  		    (!test_bit(IPOIB_MCAST_FLAG_SENDONLY, &mcast->flags) ||
> @@ -621,7 +630,8 @@ void ipoib_mcast_join_task(struct work_struct *work)
>  				init_completion(&mcast->done);
>  				set_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags);
>  				spin_unlock_irq(&priv->lock);
> -				ipoib_mcast_join(dev, mcast);
> +				if (ipoib_mcast_join(dev, mcast) != 0)

3. There is no need to compare with 0. Just use "if (ipoib...(...))"
construction.

> +					return;
>  				spin_lock_irq(&priv->lock);
>  			} else if (!delay_until ||
>  				 time_before(mcast->delay_until, delay_until))
> 
> --
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