lkml.org 
[lkml]   [2015]   [Sep]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: Warning in irq_work_queue_on()
On Thu, Sep 03, 2015 at 12:24:27AM +0200, Peter Zijlstra wrote:
> On Wed, Sep 02, 2015 at 11:50:22PM +0200, Frederic Weisbecker wrote:
> > > > [ 875.703227] [<ffffffff810c2d74>] tick_nohz_full_kick_cpu+0x44/0x50
> >
> > It happens in nohz full, but I'm not sure the guilty is nohz full.
> >
> > The problem here is that wake_up_nohz_cpu() selects a CPU that is offline.
>
> wake_up_nohz_cpu() doesn't do any such thing. Where does the selection
> logic live?

Err, got confused with get_nohz_timer_target(). But yeah wake_up_nohz_cpu() is
called with a CPU that is chosen by mod_timer() -> get_nohz_timer_target().

>
> > But this shouldn't happen. Either it selects a CPU that is in the domain tree,
> > and I suspect offline CPUs aren't supposed to be there, or it selects the current
> > CPU. And if the CPU is offlined, it shouldn't be running some kthread...
>
> Do no assume things like that.. always check with the active mask.

Hmm, so perhaps we need something like this (makes me realize that
the is_housekeeping_cpu() passes the wrong argument, no issue in practice
since nohz full aren't in the domain tree but I still need to fix that along).

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0902e4d..2c10a69 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -628,7 +628,7 @@ int get_nohz_timer_target(void)

rcu_read_lock();
for_each_domain(cpu, sd) {
- for_each_cpu(i, sched_domain_span(sd)) {
+ for_each_cpu_and(i, sched_domain_span(sd), cpu_online_mask) {
if (!idle_cpu(i) && is_housekeeping_cpu(cpu)) {
cpu = i;
goto unlock;


\
 
 \ /
  Last update: 2015-09-03 02:21    [W:0.105 / U:0.372 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site