Messages in this thread | | | Date | Thu, 9 Oct 2008 19:13:02 -0700 | From | "Paul E. McKenney" <> | Subject | Re: kernel BUG at kernel/sched_rt.c:322! |
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On Fri, Oct 10, 2008 at 09:54:11AM +0800, Zhang, Yanmin wrote: > > On Thu, 2008-10-09 at 05:31 -0700, Paul E. McKenney wrote: > > On Thu, Oct 09, 2008 at 07:06:38AM +0200, Peter Zijlstra wrote: > > > On Wed, 2008-10-08 at 18:14 -0700, Paul E. McKenney wrote: > > > > When I enable: > > > > > > > > CONFIG_GROUP_SCHED=y > > > > CONFIG_FAIR_GROUP_SCHED=y > > > > CONFIG_USER_SCHED=y > > > > > > > > and run a bash script onlining and offlining CPUs in an infinite loop > > > > on x86 using 2.6.27-rc9, after about 1.5 hours I get the following. > Paul, > > Wuld you like to share your scipt? I tested cpu hotplug on my 8-core machine by > unplug cpu 2~5 and plug them in a loop for one night and didn't trigger the issue.
See attached! I hand-edit the loop for the machine at hand, so on an 8-CPU x86 machine I would use "for ((i = 1; i < 8; i++))", given that x86 machines tend not to allow you to offline CPU 0.
> Did you set CONFIG_RT_GROUP_SCHED=y?
No, I did not.
Thanx, Paul
> > > > On the off-chance that this is new news... > > > > > > Hmm, yes. I thought I had all those fixed :-( > > > > I know that feeling!!! ;-) > > > > > > [ 5538.091011] kernel BUG at kernel/sched_rt.c:322! > > > > [ 5538.091011] invalid opcode: 0000 [#1] SMP > > > > [ 5538.091011] Modules linked in: > > > > [ 5538.091011] > > > > [ 5538.091011] Pid: 2819, comm: sh Not tainted (2.6.27-rc9-autokern1 #1) > > > > [ 5538.091011] EIP: 0060:[<c011c287>] EFLAGS: 00010002 CPU: 7 > > > > [ 5538.091011] EIP is at __disable_runtime+0x1c7/0x1d0 > > > > [ 5538.091011] EAX: c9056eec EBX: 00000001 ECX: 00000008 EDX: 00006060 > > > > [ 5538.091011] ESI: 02faf080 EDI: 00000000 EBP: f6df7cd0 ESP: f6df7ca8 > > > > [ 5538.091011] DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 > > > > [ 5538.091011] Process sh (pid: 2819, ti=f6df6000 task=f6cbdc00 task.ti=f6df6000) > > > > [ 5538.091011] Stack: f68c8004 c9056eec f68c8000 c9056b98 00000008 5d353631 c04d0020 c9056b00 > > > > [ 5538.091011] c9056b00 c9056b00 f6df7cdc c011d151 c037dfc0 f6df7cec c011aedb f68c8000 > > > > [ 5538.091011] c04d2200 f6df7d04 c011f967 00000282 00000000 00000000 00000000 f6df7e48 > > > > [ 5538.091011] Call Trace: > > > > [ 5538.091011] [<c011d151>] ? rq_offline_rt+0x21/0x60 > > > > [ 5538.091011] [<c011aedb>] ? set_rq_offline+0x2b/0x50 > > > > [ 5538.091011] [<c011f967>] ? rq_attach_root+0xa7/0xb0 > > > > [ 5538.091011] [<c0120bbf>] ? cpu_attach_domain+0x30f/0x490 > > > > > > At the very least we're doing part of the offline process twice it > > > seems, once through set_rq_offline()/set_rq_online() and once through > > > disable_runtime()/enabled_runtime(). > > > > > > But seeing as we set an offlined cpu's runtime to RUNTIME_INF and skip > > > cpus with RUNTIME_INF runtime that should be harmless. > > > > Would double-processing a non-offlined CPU cause trouble, perhaps > > setting the runtime to a nonsensical value? > > > > > Modifications to rt_rq->rt_runtime are all done while holding > > > rt_b->rt_runtime_lock and rt_rq->rt_runtime_lock (do_balance_runtime() > > > and __disable_runtime() and __enable_runtime()). Which means its enough > > > to hold either of those locks in order to get a stable reading of the > > > value. > These locks, especially rt_b->rt_runtime_lock, prevent the simultaneous > changing of rt_runtime. It looks codes are ok. > > Anything related to RCU? > > > > > > > Which leaves me puzzled for the moment... > > > > I know that feeling as well... > > > > > tip/master has the following commit to clarify the code somewhat: > > > > > > > > > commit 78333cdd0e472180743d35988e576d6ecc6f6ddb > > > Author: Peter Zijlstra <a.p.zijlstra@chello.nl> > > > Date: Tue Sep 23 15:33:43 2008 +0200 > > > > > > sched: add some comments to the bandwidth code > > > > > > Hopefully clarify some of this code a little. > > > > > > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> > > > Signed-off-by: Ingo Molnar <mingo@elte.hu> > > > > > > diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c > > > index 2e228bd..d570a8c 100644 > > > --- a/kernel/sched_rt.c > > > +++ b/kernel/sched_rt.c > > > @@ -231,6 +231,9 @@ static inline struct rt_bandwidth *sched_rt_bandwidth(struct rt_rq *rt_rq) > > > #endif /* CONFIG_RT_GROUP_SCHED */ > > > > > > #ifdef CONFIG_SMP > > > +/* > > > + * We ran out of runtime, see if we can borrow some from our neighbours. > > > + */ > > > > Suppose that all CPUs nearby have run out of runtime. Or is that > > possible? > > > > Thanx, Paul > > > > > static int do_balance_runtime(struct rt_rq *rt_rq) > > > { > > > struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq); > > > @@ -250,9 +253,18 @@ static int do_balance_runtime(struct rt_rq *rt_rq) > > > continue; > > > > > > spin_lock(&iter->rt_runtime_lock); > > > + /* > > > + * Either all rqs have inf runtime and there's nothing to steal > > > + * or __disable_runtime() below sets a specific rq to inf to > > > + * indicate its been disabled and disalow stealing. > > > + */ > > > if (iter->rt_runtime == RUNTIME_INF) > > > goto next; > > > > > > + /* > > > + * From runqueues with spare time, take 1/n part of their > > > + * spare time, but no more than our period. > > > + */ > > > diff = iter->rt_runtime - iter->rt_time; > > > if (diff > 0) { > > > diff = div_u64((u64)diff, weight); > > > @@ -274,6 +286,9 @@ next: > > > return more; > > > } > > > > > > +/* > > > + * Ensure this RQ takes back all the runtime it lend to its neighbours. > > > + */ > > > static void __disable_runtime(struct rq *rq) > > > { > > > struct root_domain *rd = rq->rd; > > > @@ -289,17 +304,33 @@ static void __disable_runtime(struct rq *rq) > > > > > > spin_lock(&rt_b->rt_runtime_lock); > > > spin_lock(&rt_rq->rt_runtime_lock); > > > + /* > > > + * Either we're all inf and nobody needs to borrow, or we're > > > + * already disabled and thus have nothing to do, or we have > > > + * exactly the right amount of runtime to take out. > > > + */ > > > if (rt_rq->rt_runtime == RUNTIME_INF || > > > rt_rq->rt_runtime == rt_b->rt_runtime) > > > goto balanced; > > > spin_unlock(&rt_rq->rt_runtime_lock); > > > > > > + /* > > > + * Calculate the difference between what we started out with > > > + * and what we current have, that's the amount of runtime > > > + * we lend and now have to reclaim. > > > + */ > > > want = rt_b->rt_runtime - rt_rq->rt_runtime; > > > > > > + /* > > > + * Greedy reclaim, take back as much as we can. > > > + */ > > > for_each_cpu_mask(i, rd->span) { > > > struct rt_rq *iter = sched_rt_period_rt_rq(rt_b, i); > > > s64 diff; > > > > > > + /* > > > + * Can't reclaim from ourselves or disabled runqueues. > > > + */ > > > if (iter == rt_rq || iter->rt_runtime == RUNTIME_INF) > > > continue; > > > > > > @@ -319,8 +350,16 @@ static void __disable_runtime(struct rq *rq) > > > } > > > > > > spin_lock(&rt_rq->rt_runtime_lock); > > > + /* > > > + * We cannot be left wanting - that would mean some runtime > > > + * leaked out of the system. > > > + */ > > > BUG_ON(want); > > > balanced: > > > + /* > > > + * Disable all the borrow logic by pretending we have inf > > > + * runtime - in which case borrowing doesn't make sense. > > > + */ > > > rt_rq->rt_runtime = RUNTIME_INF; > > > spin_unlock(&rt_rq->rt_runtime_lock); > > > spin_unlock(&rt_b->rt_runtime_lock); > > > @@ -343,6 +382,9 @@ static void __enable_runtime(struct rq *rq) > > > if (unlikely(!scheduler_running)) > > > return; > > > > > > + /* > > > + * Reset each runqueue's bandwidth settings > > > + */ > > > for_each_leaf_rt_rq(rt_rq, rq) { > > > struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq); > > [unhandled content-type:application/x-sh] | |