Messages in this thread | | | From | Lai Jiangshan <> | Date | Mon, 1 Aug 2022 16:48:16 +0800 | Subject | Re: [PATCH] workqueue: Use active mask for new worker when pool is DISASSOCIATED |
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On Mon, Aug 1, 2022 at 1:08 PM Schspa Shi <schspa@gmail.com> wrote: > > > 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. >
wake_up_process() will modify the task's cpumask and select a fallback cpu. The schedule code does it for all kthreads that happen to have a single CPU affinity which is lost.
> 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 >
How long will it take to reproduce the bug? I have tested for a short time on the non-rt kernel, no thing has happened yet.
> 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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