On Mon, Apr 02, 2018 at 03:04:38PM -0700, Paul E. McKenney wrote: > The WARN_ON_ONCE() triggering is this guy: > > delta = rq_clock_task(rq) - curr->se.exec_start; > WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3); > > But given that ->se.exec_start is zeroed from time to time, for example, > in migrate_task_rq_fair(), I am a bit suspicious of this check. > > What am I missing here?
We clear it on migration, but set it when we schedule a task back in. The above checks that the 'current' task of that CPU had a tick at least 3 seconds ago (to ensure tasks don't go too long without ticks). The 'current' task is obviously scheduled in and thus must have !0 exec_start time.
