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um: do not send SIGALRM to userspace in time-travel mode

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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 <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20250408074524.300153-1-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
This commit is contained in:
Benjamin Berg 2025-04-08 09:45:23 +02:00 committed by Johannes Berg
parent 82c8e1280c
commit 49caacf100
1 changed files with 9 additions and 4 deletions
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13
arch/um/kernel/time.c
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@ -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);