On 01/11/2017 08:19 PM, Parthasarathy Bhuvaragan wrote:
> We trigger a soft lockup as we grab nametbl_lock twice if the node
> has a pending node up/down or link up/down event while:
> - we process an incoming named message in tipc_named_rcv() and
> perform an tipc_update_nametbl().
> - we have pending backlog items in the name distributor queue
> during a nametable update using tipc_nametbl_publish() or
> tipc_nametbl_withdraw().
>
> The following are the call chain associated:
> tipc_named_rcv() Grabs nametbl_lock
> tipc_update_nametbl() (publish/withdraw)
> tipc_node_subscribe()/unsubscribe()
> tipc_node_write_unlock()
> << lockup occurs if an outstanding node/link event
> exits, as we grabs nametbl_lock again >>
>
> tipc_nametbl_withdraw() Grab nametbl_lock
> tipc_named_process_backlog()
> tipc_update_nametbl()
> << rest as above >>
>
> The function tipc_node_write_unlock(), in addition to releasing the
> lock processes the outstanding node/link up/down events. To do this,
> we need to grab the nametbl_lock again leading to the lockup.
>
> In this commit we fix the soft lockup by introducing a fast variant of
> node_unlock(), where we just release the lock. We adapt the
> node_subscribe()/node_unsubscribe() to use the fast variants.
>
> Signed-off-by: Parthasarathy Bhuvaragan
> <parthasarathy.bhuvara...@ericsson.com>
Acked-by: Ying Xue <ying....@windriver.com>
> ---
> net/tipc/node.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/net/tipc/node.c b/net/tipc/node.c
> index 2883f6a0ed98..796dec65944a 100644
> --- a/net/tipc/node.c
> +++ b/net/tipc/node.c
> @@ -263,6 +263,11 @@ static void tipc_node_write_lock(struct tipc_node *n)
> write_lock_bh(&n->lock);
> }
>
> +static void tipc_node_write_unlock_fast(struct tipc_node *n)
> +{
> + write_unlock_bh(&n->lock);
> +}
> +
> static void tipc_node_write_unlock(struct tipc_node *n)
> {
> struct net *net = n->net;
> @@ -417,7 +422,7 @@ void tipc_node_subscribe(struct net *net, struct
> list_head *subscr, u32 addr)
> }
> tipc_node_write_lock(n);
> list_add_tail(subscr, &n->publ_list);
> - tipc_node_write_unlock(n);
> + tipc_node_write_unlock_fast(n);
> tipc_node_put(n);
> }
>
> @@ -435,7 +440,7 @@ void tipc_node_unsubscribe(struct net *net, struct
> list_head *subscr, u32 addr)
> }
> tipc_node_write_lock(n);
> list_del_init(subscr);
> - tipc_node_write_unlock(n);
> + tipc_node_write_unlock_fast(n);
> tipc_node_put(n);
> }
>
>
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