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SubjectRe: 4.14: WARNING: CPU: 4 PID: 2895 at block/blk-mq.c:1144 with virtio-blk (also 4.12 stable)
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On 12/07/2017 12:29 AM, Christoph Hellwig wrote:
> On Wed, Dec 06, 2017 at 01:25:11PM +0100, Christian Borntraeger wrote:
> t > commit 11b2025c3326f7096ceb588c3117c7883850c068 -> bad
>> blk-mq: create a blk_mq_ctx for each possible CPU
>> does not boot on DASD and
>> commit 9c6ae239e01ae9a9f8657f05c55c4372e9fc8bcc -> good
>> genirq/affinity: assign vectors to all possible CPUs
>> does boot with DASD disks.
>>
>> Also adding Stefan Haberland if he has an idea why this fails on DASD and adding Martin (for the
>> s390 irq handling code).
>
> That is interesting as it really isn't related to interrupts at all,
> it just ensures that possible CPUs are set in ->cpumask.
>
> I guess we'd really want:
>
> e005655c389e3d25bf3e43f71611ec12f3012de0
> "blk-mq: only select online CPUs in blk_mq_hctx_next_cpu"
>
> before this commit, but it seems like the whole stack didn't work for
> your either.
>
> I wonder if there is some weird thing about nr_cpu_ids in s390?

The problem starts as soon as NR_CPUS is larger than the number
of real CPUs.

Aquestions Wouldnt your change in blk_mq_hctx_next_cpu fail if there is more than 1 non-online cpu:

e.g. dont we need something like (whitespace and indent damaged)

@@ -1241,11 +1241,11 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
if (--hctx->next_cpu_batch <= 0) {
int next_cpu;

+ do {
next_cpu = cpumask_next(hctx->next_cpu, hctx->cpumask);
- if (!cpu_online(next_cpu))
- next_cpu = cpumask_next(next_cpu, hctx->cpumask);
if (next_cpu >= nr_cpu_ids)
next_cpu = cpumask_first(hctx->cpumask);
+ } while (!cpu_online(next_cpu));

hctx->next_cpu = next_cpu;
hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;

it does not fix the issue, though (and it would be pretty inefficient for large NR_CPUS)


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