Messages in this thread Patch in this message | | | Date | Wed, 08 Jun 2005 00:09:09 +1000 | From | Nick Piggin <> | Subject | Re: Hang in sched_balance_self() |
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Jack Steiner wrote: > Nick - > > The latest 2.6.12-rc5-mm2 tree fails to boot on some of the 64p > SGI systems. The system hangs immediately after printing: > > ... > Inode-cache hash table entries: 8388608 (order: 12, 67108864 bytes) > Mount-cache hash table entries: 1024 > Boot processor id 0x0/0x0 > Brought up 64 CPUs > Total of 64 processors activated (118415.36 BogoMIPS). > > > I have isolated the failure to cpu 0 hanging in sched_balance_self() during > a fork (or clone). The "while" loop at the end of function never > terminates, ie. sd is never NULL. > > Is this a problem that you have seen before. If not, I'll do some > more digging & isolate the problem. >
Hi Jack, I haven't completely got to the bottom of this yet, but I was able to reproduce on a 64-way Altix, and something like the attached patch seems to 'fix' the problem.
I didn't have time to find what's gone wrong tonight, but I'll get to that tomorrow.
-- SUSE Labs, Novell Inc.
Index: linux-2.6/kernel/sched.c =================================================================== --- linux-2.6.orig/kernel/sched.c 2005-06-08 00:01:53.000000000 +1000 +++ linux-2.6/kernel/sched.c 2005-06-08 00:02:47.000000000 +1000 @@ -1113,6 +1113,7 @@ static int sched_balance_self(int cpu, i cpumask_t span; struct sched_group *group; int new_cpu; + int weight; span = sd->span; group = find_idlest_group(sd, t, cpu); @@ -1127,8 +1128,9 @@ static int sched_balance_self(int cpu, i cpu = new_cpu; nextlevel: sd = NULL; + weight = cpus_weight(span); for_each_domain(cpu, tmp) { - if (cpus_subset(span, tmp->span)) + if (weight <= cpus_weight(tmp->span)) break; if (tmp->flags & flag) sd = tmp; | |