Re: [PATCH] IPoIB: Fix race in deleting ipoib_neigh entries

[Jim Foraker <foraker1-i2BcT+NCU+M@public.gmane.org>]

     BTW, I believe this is an alternate fix for the bug previously
documented on the list here:
http://marc.info/?l=linux-rdma&m=136881939301117&w=2.  

     Jim

On Thu, 2013-08-08 at 17:44 -0700, Jim Foraker wrote:
> In several places, this snippet is used when removing neigh entries:
> 
> 	list_del(&neigh->list);
> 	ipoib_neigh_free(neigh);
> 
> The list_del() removes neigh from the associated struct ipoib_path, while
> ipoib_neigh_free() removes neigh from the device's neigh entry lookup
> table.  Both of these operations are protected by the priv->lock
> spinlock.  The table however is also protected via RCU, and so naturally
> the lock is not held when doing reads.
> 
> This leads to a race condition, in which a thread may successfully look
> up a neigh entry that has already been deleted from neigh->list.  Since
> the previous deletion will have marked the entry with poison, a second
> list_del() on the object will cause a panic:
> 
>   #5 [ffff8802338c3c70] general_protection at ffffffff815108c5
>      [exception RIP: list_del+16]
>      RIP: ffffffff81289020  RSP: ffff8802338c3d20  RFLAGS: 00010082
>      RAX: dead000000200200  RBX: ffff880433e60c88  RCX: 0000000000009e6c
>      RDX: 0000000000000246  RSI: ffff8806012ca298  RDI: ffff880433e60c88
>      RBP: ffff8802338c3d30   R8: ffff8806012ca2e8   R9: 00000000ffffffff
>      R10: 0000000000000001  R11: 0000000000000000  R12: ffff8804346b2020
>      R13: ffff88032a3e7540  R14: ffff8804346b26e0  R15: 0000000000000246
>      ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0000
>   #6 [ffff8802338c3d38] ipoib_cm_tx_handler at ffffffffa066fe0a [ib_ipoib]
>   #7 [ffff8802338c3d98] cm_process_work at ffffffffa05149a7 [ib_cm]
>   #8 [ffff8802338c3de8] cm_work_handler at ffffffffa05161aa [ib_cm]
>   #9 [ffff8802338c3e38] worker_thread at ffffffff81090e10
>  #10 [ffff8802338c3ee8] kthread at ffffffff81096c66
>  #11 [ffff8802338c3f48] kernel_thread at ffffffff8100c0ca
> 
> We move the list_del() into ipoib_neigh_free(), so that deletion happens
> only once, after the entry has been successfully removed from the lookup
> table.  This same behavior is already used in ipoib_del_neighs_by_gid()
> and __ipoib_reap_neigh().
> 
> Signed-off-by: Jim Foraker <foraker1-i2BcT+NCU+M@public.gmane.org>
> ---
>  drivers/infiniband/ulp/ipoib/ipoib_cm.c   |    3 ---
>  drivers/infiniband/ulp/ipoib/ipoib_main.c |    9 +++------
>  2 files changed, 3 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/infiniband/ulp/ipoib/ipoib_cm.c b/drivers/infiniband/ulp/ipoib/ipoib_cm.c
> index 3eceb61..7a31754 100644
> --- a/drivers/infiniband/ulp/ipoib/ipoib_cm.c
> +++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c
> @@ -817,7 +817,6 @@ void ipoib_cm_handle_tx_wc(struct net_device *dev, struct ib_wc *wc)
>  
>  		if (neigh) {
>  			neigh->cm = NULL;
> -			list_del(&neigh->list);
>  			ipoib_neigh_free(neigh);
>  
>  			tx->neigh = NULL;
> @@ -1234,7 +1233,6 @@ static int ipoib_cm_tx_handler(struct ib_cm_id *cm_id,
>  
>  		if (neigh) {
>  			neigh->cm = NULL;
> -			list_del(&neigh->list);
>  			ipoib_neigh_free(neigh);
>  
>  			tx->neigh = NULL;
> @@ -1325,7 +1323,6 @@ static void ipoib_cm_tx_start(struct work_struct *work)
>  			neigh = p->neigh;
>  			if (neigh) {
>  				neigh->cm = NULL;
> -				list_del(&neigh->list);
>  				ipoib_neigh_free(neigh);
>  			}
>  			list_del(&p->list);
> diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> index c6f71a8..82cec1a 100644
> --- a/drivers/infiniband/ulp/ipoib/ipoib_main.c
> +++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> @@ -493,7 +493,6 @@ static void path_rec_completion(int status,
>  									       path,
>  									       neigh));
>  				if (!ipoib_cm_get(neigh)) {
> -					list_del(&neigh->list);
>  					ipoib_neigh_free(neigh);
>  					continue;
>  				}
> @@ -618,7 +617,6 @@ static void neigh_add_path(struct sk_buff *skb, u8 *daddr,
>  			if (!ipoib_cm_get(neigh))
>  				ipoib_cm_set(neigh, ipoib_cm_create_tx(dev, path, neigh));
>  			if (!ipoib_cm_get(neigh)) {
> -				list_del(&neigh->list);
>  				ipoib_neigh_free(neigh);
>  				goto err_drop;
>  			}
> @@ -639,7 +637,7 @@ static void neigh_add_path(struct sk_buff *skb, u8 *daddr,
>  		neigh->ah  = NULL;
>  
>  		if (!path->query && path_rec_start(dev, path))
> -			goto err_list;
> +			goto err_path;
>  
>  		__skb_queue_tail(&neigh->queue, skb);
>  	}
> @@ -648,9 +646,6 @@ static void neigh_add_path(struct sk_buff *skb, u8 *daddr,
>  	ipoib_neigh_put(neigh);
>  	return;
>  
> -err_list:
> -	list_del(&neigh->list);
> -
>  err_path:
>  	ipoib_neigh_free(neigh);
>  err_drop:
> @@ -1098,6 +1093,8 @@ void ipoib_neigh_free(struct ipoib_neigh *neigh)
>  			rcu_assign_pointer(*np,
>  					   rcu_dereference_protected(neigh->hnext,
>  								     lockdep_is_held(&priv->lock)));
> +			/* remove from parent list */
> +			list_del(&neigh->list);
>  			call_rcu(&neigh->rcu, ipoib_neigh_reclaim);
>  			return;
>  		} else {

--
To unsubscribe from this list: send the line "unsubscribe linux-rdma" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html