lkml.org 
[lkml]   [2015]   [Jun]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: call_rcu from trace_preempt
    On Tue, 16 Jun 2015 10:20:05 -0700
    Alexei Starovoitov <ast@plumgrid.com> wrote:

    > On 6/16/15 5:38 AM, Daniel Wagner wrote:
    > > static int free_thread(void *arg)
    > > +{
    > > + unsigned long flags;
    > > + struct htab_elem *l;
    > > +
    > > + while (!kthread_should_stop()) {
    > > + spin_lock_irqsave(&elem_freelist_lock, flags);
    > > + while (!list_empty(&elem_freelist)) {
    > > + l = list_entry(elem_freelist.next,
    > > + struct htab_elem, list);
    > > + list_del(&l->list);
    > > + kfree(l);
    >
    > that's not right, since such thread defeats rcu protection of lookup.
    > We need either kfree_rcu/call_rcu or synchronize_rcu.
    > Obviously the former is preferred that's why I'm still digging into it.
    > Probably a thread that does kfree_rcu would be ok, but we shouldn't
    > be doing it unconditionally. For all networking programs and 99%
    > of tracing programs the existing code is fine and I don't want to
    > slow it down to tackle the corner case.
    > Extra spin_lock just to add it to the list is also quite costly.

    Use a irq_work() handler to do the kfree_rcu(), and use llist (lockless
    list) to add items to the list.

    -- Steve


    \
     
     \ /
      Last update: 2015-06-16 20:01    [W:2.858 / U:0.044 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site