Peter Zijlstra <[email protected]> writes: > On Fri, May 16, 2014 at 12:38:21PM +0400, Roman Gushchin wrote: > >> I still think, there is a deadlock. I'll try to explain. >> Three CPUs must be involved: >> CPU0 CPU1 CPU2 >> take rq->lock period timer fired >> ... take cfs_b lock >> ... ... >> tg_set_cfs_bandwidth() >> throttle_cfs_rq() release cfs_b lock take cfs_b lock >> ... distribute_cfs_runtime() timer_active = 0 >> take cfs_b->lock wait for rq->lock ... >> __start_cfs_bandwidth() >> {wait for timer callback >> break if timer_active == 1} >> >> So, CPU0 and CPU1 are deadlocked. > > OK, so can someone explain this ->timer_active thing? esp. what's the > 'obvious' difference with hrtimer_active()?
timer_active is only changed or checked under cfs_b lock, so that we can be certain that the timer is active whenever runtime isn't full. We can't use hrtimer_active because the timer might have unlocked the cfs_b on another cpu and be about to return HRTIMER_NORESTART. > > > Ideally we'd change the lot to not have this, but if we have to keep it > we'll need to make it lockdep visible because all this stinks -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
