[PATCH v2] timers/migration: Fix ignored event due to missing CPU update

[Frederic Weisbecker]

Le Tue, Apr 02, 2024 at 11:52:23AM +0200, Anna-Maria Behnsen a écrit :
> Frederic Weisbecker <frederic@xxxxxxxxxx> writes:
> 
> > When a group event is updated with its expiry unchanged but a different
> > CPU, that target change may go unnoticed and the event may be propagated
> > up with a stale CPU value. The following depicts a scenario that has
> > been actually observed:
> 
> urgh...
> 
> >
> > Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
> > ---
> >  kernel/time/timer_migration.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c
> > index c63a0afdcebe..90786bb9a607 100644
> > --- a/kernel/time/timer_migration.c
> > +++ b/kernel/time/timer_migration.c
> > @@ -762,8 +762,11 @@ bool tmigr_update_events(struct tmigr_group *group, struct tmigr_group *child,
> >  	 * queue when the expiry time changed only or when it could be ignored.
> >  	 */
> >  	if (timerqueue_node_queued(&evt->nextevt)) {
> > -		if ((evt->nextevt.expires == nextexp) && !evt->ignore)
> > +		if ((evt->nextevt.expires == nextexp) && !evt->ignore) {
> > +			if (evt->cpu != first_childevt->cpu)
> > +				evt->cpu = first_childevt->cpu;
> 
> Why not just unconditionally overwriting the evt->cpu value here?

Right! See below:

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