[lkml]   [2018]   [Apr]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Subjectcpu stopper threads and load balancing leads to deadlock
Hi guys,

We've seen a bug in one of our SLE kernels where the cpu stopper
thread ("migration/15") is entering idle balance. This then triggers
active load balance.

At the same time, a task on another CPU triggers a page fault and NUMA
balancing kicks in to try and migrate the task closer to the NUMA node
for that page (we're inside stop_two_cpus()). This faulting task is
spinning in try_to_wake_up() (inside smp_cond_load_acquire(&p->on_cpu,
!VAL)), waiting for "migration/15" to context switch.

Unfortunately, because "migration/15" is doing active load balance
it's spinning waiting for the NUMA-page-faulting CPU's stopper lock,
which is already held (since it's inside stop_two_cpus()).

Deadlock ensues.

This seems like a situation that should be prohibited, but I cannot
find any code to prevent it. Is it OK for stopper threads to load
balance? Is there something that should prevent this situation from

 \ /
  Last update: 2018-04-17 16:22    [W:0.124 / U:3.000 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site