From: Sergey Senozhatsky senozhatsky@chromium.org
[ Upstream commit ccfc9dd6914feaa9a81f10f9cce56eb0f7712264 ]
The soft watchdog timer function checks if a virtual machine was suspended and hence what looks like a lockup in fact is a false positive.
This is what kvm_check_and_clear_guest_paused() does: it tests guest PVCLOCK_GUEST_STOPPED (which is set by the host) and if it's set then we need to touch all watchdogs and bail out.
Watchdog timer function runs from IRQ, so PVCLOCK_GUEST_STOPPED check works fine.
There is, however, one more watchdog that runs from IRQ, so watchdog timer fn races with it, and that watchdog is not aware of PVCLOCK_GUEST_STOPPED - RCU stall detector.
apic_timer_interrupt() smp_apic_timer_interrupt() hrtimer_interrupt() __hrtimer_run_queues() tick_sched_timer() tick_sched_handle() update_process_times() rcu_sched_clock_irq()
This triggers RCU stalls on our devices during VM resume.
If tick_sched_handle()->rcu_sched_clock_irq() runs on a VCPU before watchdog_timer_fn()->kvm_check_and_clear_guest_paused() then there is nothing on this VCPU that touches watchdogs and RCU reads stale gp stall timestamp and new jiffies value, which makes it think that RCU has stalled.
Make RCU stall watchdog aware of PVCLOCK_GUEST_STOPPED and don't report RCU stalls when we resume the VM.
Signed-off-by: Sergey Senozhatsky senozhatsky@chromium.org Signed-off-by: Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/rcu/tree_stall.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 59b95cc5cbdf..4aaa4a12e95f 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -7,6 +7,8 @@ * Author: Paul E. McKenney paulmck@linux.ibm.com */
+#include <linux/kvm_para.h> + ////////////////////////////////////////////////////////////////////////////// // // Controlling CPU stall warnings, including delay calculation. @@ -695,6 +697,14 @@ static void check_cpu_stall(struct rcu_data *rdp) (READ_ONCE(rnp->qsmask) & rdp->grpmask) && cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
+ /* + * If a virtual machine is stopped by the host it can look to + * the watchdog like an RCU stall. Check to see if the host + * stopped the vm. + */ + if (kvm_check_and_clear_guest_paused()) + return; + /* We haven't checked in, so go dump stack. */ print_cpu_stall(gps); if (READ_ONCE(rcu_cpu_stall_ftrace_dump)) @@ -704,6 +714,14 @@ static void check_cpu_stall(struct rcu_data *rdp) ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) && cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
+ /* + * If a virtual machine is stopped by the host it can look to + * the watchdog like an RCU stall. Check to see if the host + * stopped the vm. + */ + if (kvm_check_and_clear_guest_paused()) + return; + /* They had a few time units to dump stack, so complain. */ print_other_cpu_stall(gs2, gps); if (READ_ONCE(rcu_cpu_stall_ftrace_dump))