• Zoltan Kiss's avatar
    xen-netback: Fix Rx stall due to race condition · 9ab9831b
    Zoltan Kiss authored
    The recent patch to fix receive side flow control
    (11b57f90
    
    : xen-netback: stop vif thread
    spinning if frontend is unresponsive) solved the spinning thread problem,
    however caused an another one. The receive side can stall, if:
    - [THREAD] xenvif_rx_action sets rx_queue_stopped to true
    - [INTERRUPT] interrupt happens, and sets rx_event to true
    - [THREAD] then xenvif_kthread sets rx_event to false
    - [THREAD] rx_work_todo doesn't return true anymore
    
    Also, if interrupt sent but there is still no room in the ring, it take quite a
    long time until xenvif_rx_action realize it. This patch ditch that two variable,
    and rework rx_work_todo. If the thread finds it can't fit more skb's into the
    ring, it saves the last slot estimation into rx_last_skb_slots, otherwise it's
    kept as 0. Then rx_work_todo will check if:
    - there is something to send to the ring (like before)
    - there is space for the topmost packet in the queue
    
    I think that's more natural and optimal thing to test than two bool which are
    set somewhere else.
    Signed-off-by: default avatarZoltan Kiss <zoltan.kiss@citrix.com>
    Reviewed-by: default avatarPaul Durrant <paul.durrant@citrix.com>
    Acked-by: default avatarWei Liu <wei.liu2@citrix.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    9ab9831b