5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Nicholas Piggin npiggin@gmail.com
[ Upstream commit 98f887f820c993e05a12e8aa816c80b8661d4c87 ]
On a ~2000 CPU powerpc system, hard lockups have been observed in the workqueue code when stop_machine runs (in this case due to CPU hotplug). This is due to lots of CPUs spinning in multi_cpu_stop, calling touch_nmi_watchdog() which ends up calling wq_watchdog_touch(). wq_watchdog_touch() writes to the global variable wq_watchdog_touched, and that can find itself in the same cacheline as other important workqueue data, which slows down operations to the point of lockups.
In the case of the following abridged trace, worker_pool_idr was in the hot line, causing the lockups to always appear at idr_find.
watchdog: CPU 1125 self-detected hard LOCKUP @ idr_find Call Trace: get_work_pool __queue_work call_timer_fn run_timer_softirq __do_softirq do_softirq_own_stack irq_exit timer_interrupt decrementer_common_virt * interrupt: 900 (timer) at multi_cpu_stop multi_cpu_stop cpu_stopper_thread smpboot_thread_fn kthread
Fix this by having wq_watchdog_touch() only write to the line if the last time a touch was recorded exceeds 1/4 of the watchdog threshold.
Reported-by: Srikar Dronamraju srikar@linux.vnet.ibm.com Signed-off-by: Nicholas Piggin npiggin@gmail.com Reviewed-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Tejun Heo tj@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/workqueue.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index f7975a8f665f..73002260674f 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -5935,12 +5935,18 @@ static void wq_watchdog_timer_fn(struct timer_list *unused)
notrace void wq_watchdog_touch(int cpu) { + unsigned long thresh = READ_ONCE(wq_watchdog_thresh) * HZ; + unsigned long touch_ts = READ_ONCE(wq_watchdog_touched); + unsigned long now = jiffies; + if (cpu >= 0) - per_cpu(wq_watchdog_touched_cpu, cpu) = jiffies; + per_cpu(wq_watchdog_touched_cpu, cpu) = now; else WARN_ONCE(1, "%s should be called with valid CPU", __func__);
- wq_watchdog_touched = jiffies; + /* Don't unnecessarily store to global cacheline */ + if (time_after(now, touch_ts + thresh / 4)) + WRITE_ONCE(wq_watchdog_touched, jiffies); }
static void wq_watchdog_set_thresh(unsigned long thresh)