From 49caacf1004d1e1fc40cfab165f104d051867c6e Mon Sep 17 00:00:00 2001 From: Benjamin Berg Date: Tue, 8 Apr 2025 09:45:23 +0200 Subject: [PATCH] um: do not send SIGALRM to userspace in time-travel mode We send a SIGALRM to userspace processes to interrupt them. Really, doing so is only needed if they are actually executing at the time (to ensure we return to kernelspace). Unfortunately, we do not have that information readily available. We can however be sure that this is never the case when we are in time-travel mode with infinite CPU. Signed-off-by: Benjamin Berg Link: https://patch.msgid.link/20250408074524.300153-1-benjamin@sipsolutions.net Signed-off-by: Johannes Berg --- arch/um/kernel/time.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c index 1394568c02106..ae0fa2173778f 100644 --- a/arch/um/kernel/time.c +++ b/arch/um/kernel/time.c @@ -856,11 +856,16 @@ static struct clock_event_device timer_clockevent = { static irqreturn_t um_timer(int irq, void *dev) { - if (get_current()->mm != NULL) - { - /* userspace - relay signal, results in correct userspace timers */ + /* + * Interrupt the (possibly) running userspace process, technically this + * should only happen if userspace is currently executing. + * With infinite CPU time-travel, we can only get here when userspace + * is not executing. Do not notify there and avoid spurious scheduling. + */ + if (time_travel_mode != TT_MODE_INFCPU && + time_travel_mode != TT_MODE_EXTERNAL && + get_current()->mm) os_alarm_process(get_current()->mm->context.id.pid); - } (*timer_clockevent.event_handler)(&timer_clockevent); -- 2.47.3