On Tue, Feb 02, 2016 at 03:44:24PM +0100, Mike Galbraith wrote: > Scenario: CPU168 calls mod_delayed_work(), is taken offline before the > timer expires. Due to 874bbfe6, dwork->cpu is the now offline CPU168 > vs the previous WORK_CPU_UNBOUND, timer fires on CPU131, it tries to > __queue_work() with cpu == the now offline CPU168, gets to... > > } else > pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu)); > > ... and goes boom. > > <snippet> > crash> p numa_node | grep 168 > [168]: ffff8c03fdf0e328 > crash> rd ffff8c03fdf0e328 > ffff8c03fdf0e328: 00000000ffffffff ........ > > Thus, pwq becomes 000000000. Then, as the result of reference to > pwq->pool, NULL reference occurs at (*PANIC). > </snippet> > > What if anything is supposed to prevent this?
(cc'ing So, the root problem here is cpu <-> node mapping flipping across cpu on/offlining which is unnecessary and causes other issues too. It's being worked on for quite a while now. http://lkml.kernel.org/g/1453702100-2597-1-git-send-email-tangc...@cn.fujitsu.com I'll create a bandaid patch for now so that wq falls back to dfl_wq on negative node. Thanks. -- tejun
