On 09/08/2019 14:33, Phil Auld wrote: > On Tue, Aug 06, 2019 at 03:03:34PM +0200 Peter Zijlstra wrote: >> On Thu, Aug 01, 2019 at 09:37:49AM -0400, Phil Auld wrote: >>> Enabling WARN_DOUBLE_CLOCK in /sys/kernel/debug/sched_features causes >> >> ISTR there were more issues; but it sure is good to start picking them >> off. >> > > Following up on this I hit another in rt.c which looks like: > > [ 156.348854] Call Trace: > [ 156.351301] <IRQ> > [ 156.353322] sched_rt_period_timer+0x124/0x350 > [ 156.357766] ? sched_rt_rq_enqueue+0x90/0x90 > [ 156.362037] __hrtimer_run_queues+0xfb/0x270 > [ 156.366303] hrtimer_interrupt+0x122/0x270 > [ 156.370403] smp_apic_timer_interrupt+0x6a/0x140 > [ 156.375022] apic_timer_interrupt+0xf/0x20 > [ 156.379119] </IRQ> > > It looks like the same issue of not using the rq_lock* wrappers and > hence not using the pinning. From looking at the code there is at > least one potential hit in deadline.c in the push_dl_task path with > find_lock_later_rq but I have not hit that in practice. > > This commit, which introduced the warning, seems to imply that the use > of the rq_lock* wrappers is required, at least for any sections that will > call update_rq_clock: > > commit 26ae58d23b94a075ae724fd18783a3773131cfbc > Author: Peter Zijlstra <pet...@infradead.org> > Date: Mon Oct 3 16:53:49 2016 +0200 > > sched/core: Add WARNING for multiple update_rq_clock() calls > > Now that we have no missing calls, add a warning to find multiple > calls. > > By having only a single update_rq_clock() call per rq-lock section, > the section appears 'atomic' wrt time. > > > Is that the case? Otherwise we have these false positives. >
Looks like it - only rq_pin_lock() clears RQCF_UPDATED, so any update_rq_clock() that isn't preceded by that function will still have RQCF_UPDATED set the second time it's executed and will trigger the warn. Seeing as the wrappers boil down to raw_spin_*() when the debug bits are disabled, I don't see why we wouldn't want to convert these callsites. > I can spin up patches if so. > > > Thanks, > Phil > >
