Messages in this thread | | | From | Schspa Shi <> | Subject | Re: [PATCH] workqueue: Use active mask for new worker when pool is DISASSOCIATED | Date | Mon, 01 Aug 2022 12:42:33 +0800 |
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Lai Jiangshan <jiangshanlai@gmail.com> writes:
> On Sat, Jul 30, 2022 at 12:19 PM Schspa Shi <schspa@gmail.com> wrote: >> >> >> Peter Zijlstra <peterz@infradead.org> writes: >> >> > On Wed, Jul 13, 2022 at 05:52:58PM +0800, Lai Jiangshan wrote: >> >> >> >> >> >> CC Peter. >> >> Peter has changed the CPU binding code in workqueue.c. >> > >> > [ 1622.829091] WARNING: CPU: 3 PID: 31 at kernel/sched/core.c:7756 sched_cpu_dying+0x74/0x204 >> > [ 1622.829374] CPU: 3 PID: 31 Comm: migration/3 Tainted: P O 5.10.59-rt52 #2 >> > ^^^^^^^^^^^^^^^^^^^^^ >> > >> > I think we can ignore this as being some ancient kernel. Please try >> > something recent. >> >> Hi peter: >> >> I spent a few days writing a test case and reproduced the problem on >> kernel 5.19. I think it's time for us to review the V3 patch for a fix. >> >> The V3 patch is at >> https://lore.kernel.org/all/20220714031645.28004-1-schspa@gmail.com/ >> Please help to review it. > > Because of the implementation of is_cpu_allowed(), > I am still suspicious about how the newly created worker can be woken > up in the dying cpu since it has no KTHREAD_IS_PER_CPU set. >
I think the comments of the V3 patch have explained the problem, the newly created worker runs on the dying CPU because we bind it to the dying CPU via kthread_bind_mask or set_cpus_allowed_ptr.
Please refer to the following scenarios.
CPU0 CPU1 ------------------------------------------------------------------ sched_cpu_deactivate(cpu_active_mask clear) workqueue_offline_cpu(work pool POOL_DISASSOCIATED) -- all worker will migrate to another cpu -- worker_thread -- will create new worker if pool->worklist is not empty create_worker() -- new kworker will bound to CPU0 (pool->attrs->cpumask will be mask of CPU0). kworker/0:x will running on rq
sched_cpu_dying if (rq->nr_running != 1 || rq_has_pinned_tasks(rq)) WARN(true, "Dying CPU not properly vacated!"); ---------OOPS-------------
When CPUHP_HRTIMERS_PREPARE < CPU0's state < CPUHP_AP_WORKQUEUE_ONLINE, the CPU0 still can schedule a new work, which will add a new work to pool->worklist of a dying CPU's work pool.
> Is it a dying cpu when onlining a CPU fails? I think balance_push > is not set in this case when it fails at some point during online. > But I haven't looked into the details and linked the clues. >
Not this case, there is on onlining CPU fails log in my test log.
> >> >> Test branch as: >> https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/tag/?h=v5.19-rc8-rt8 >> > > Can it only be triggered in the rt kernel? >
I only test on rt kernel, because of I work on RT kernel now, But I think non-rt kernel have the issues too.
>> I think this code is new enough to demonstrate that the problem persists. >> >> The log as fellowing: >> >> [ 3103.198684] ------------[ cut here ]------------ >> [ 3103.198684] Dying CPU not properly vacated! >> [ 3103.198684] WARNING: CPU: 1 PID: 23 at kernel/sched/core.c:9575 sched_cpu_dying.cold+0xc/0xc3 >> [ 3103.198684] Modules linked in: work_test(O) > > Could you give me the code of this module?
The module's source code is at https://github.com/schspa/code_snippet/blob/master/kernel_module/workqueue_test/work-test.c Kernel defconfig is at https://github.com/schspa/ktest/blob/main/configs/linux_rt_defconfig
I add a hook to the entry of worker_thread, which add extra 50ms delay to make it reproduced faster.
-- BRs Schspa Shi
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