4.4-stable review patch. If anyone has any objections, please let me know.
------------------ From: Vlastimil Babka <[email protected]> commit a9f2a846f0503e7d729f552e3ccfe2279010fe94 upstream. cache_reap() is initially scheduled in start_cpu_timer() via schedule_delayed_work_on(). But then the next iterations are scheduled via schedule_delayed_work(), i.e. using WORK_CPU_UNBOUND. Thus since commit ef557180447f ("workqueue: schedule WORK_CPU_UNBOUND work on wq_unbound_cpumask CPUs") there is no guarantee the future iterations will run on the originally intended cpu, although it's still preferred. I was able to demonstrate this with /sys/module/workqueue/parameters/debug_force_rr_cpu. IIUC, it may also happen due to migrating timers in nohz context. As a result, some cpu's would be calling cache_reap() more frequently and others never. This patch uses schedule_delayed_work_on() with the current cpu when scheduling the next iteration. Link: http://lkml.kernel.org/r/[email protected] Fixes: ef557180447f ("workqueue: schedule WORK_CPU_UNBOUND work on wq_unbound_cpumask CPUs") Signed-off-by: Vlastimil Babka <[email protected]> Acked-by: Pekka Enberg <[email protected]> Acked-by: Christoph Lameter <[email protected]> Cc: Joonsoo Kim <[email protected]> Cc: David Rientjes <[email protected]> Cc: Tejun Heo <[email protected]> Cc: Lai Jiangshan <[email protected]> Cc: John Stultz <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Stephen Boyd <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- mm/slab.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/mm/slab.c +++ b/mm/slab.c @@ -3915,7 +3915,8 @@ next: next_reap_node(); out: /* Set up the next iteration */ - schedule_delayed_work(work, round_jiffies_relative(REAPTIMEOUT_AC)); + schedule_delayed_work_on(smp_processor_id(), work, + round_jiffies_relative(REAPTIMEOUT_AC)); } #ifdef CONFIG_SLABINFO
