• Patrick McHardy's avatar
    [NET_SCHED]: Fix endless loops caused by inaccurate qlen counters (part 1) · 43effa1e
    Patrick McHardy authored
    There are multiple problems related to qlen adjustment that can lead
    to an upper qdisc getting out of sync with the real number of packets
    queued, leading to endless dequeueing attempts by the upper layer code.
    
    All qdiscs must maintain an accurate q.qlen counter. There are basically
    two groups of operations affecting the qlen: operations that propagate
    down the tree (enqueue, dequeue, requeue, drop, reset) beginning at the
    root qdisc and operations only affecting a subtree or single qdisc
    (change, graft, delete class). Since qlen changes during operations from
    the second group don't propagate to ancestor qdiscs, their qlen values
    become desynchronized.
    
    This patch adds a function to propagate qlen changes up the qdisc tree,
    optionally calling a callback function to perform qdisc-internal
    maintenance when the child qdisc becomes empty. The follow-up patches
    will convert all qdiscs to use this function where necessary.
    
    Noticed by Timo Steinbach <tsteinbach@astaro.com>.
    Signed-off-by: default avatarPatrick McHardy <kaber@trash.net>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    43effa1e
sch_generic.h 7.48 KB