Messages in this thread | | | Subject | Re: [PATCH] workqueue: Handle race between wake up and rebind | From | Neeraj Upadhyay <> | Date | Thu, 18 Jan 2018 15:37:20 +0530 |
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On 01/18/2018 08:32 AM, Lai Jiangshan wrote: > On Wed, Jan 17, 2018 at 4:08 AM, Neeraj Upadhyay <neeraju@codeaurora.org> wrote: >> >> On 01/16/2018 11:05 PM, Tejun Heo wrote: >>> Hello, Neeraj. >>> >>> On Mon, Jan 15, 2018 at 02:08:12PM +0530, Neeraj Upadhyay wrote: >>>> - kworker/0:0 gets chance to run on cpu1; while processing >>>> a work, it goes to sleep. However, it does not decrement >>>> pool->nr_running. This is because WORKER_REBOUND (NOT_ >>>> RUNNING) flag was cleared, when worker entered worker_ >>> Do you mean that because REBOUND was set? >> >> Actually, I meant REBOUND was not set. Below is the sequence >> >> - cpu0 bounded pool is unbound. >> >> - kworker/0:0 is woken up on cpu1. >> >> - cpu0 pool is rebound >> REBOUND is set for kworker/0:0 >> > Thanks for looking into the detail of workqueue... > > "REBOUND is set for kworker/0:0" means set_cpus_allowed_ptr(kworker/0:0) > already successfull returned and kworker/0:0 is already moved to cpu0. > > It will not still run on cpu1 as the following steps you described. > > If there is something wrong with " set_cpus_allowed_ptr()" > in this situation, could you please elaborate it.
Thanks Lai, I missed that; will debug from that perspective. > >> - kworker/0:0 starts running on cpu1 >> worker_thread() >> // It clears REBOUND and sets nr_running =1 after below call >> worker_clr_flags(worker, WORKER_PREP | WORKER_REBOUND); >> >> - kworker/0:0 goes to sleep >> wq_worker_sleeping() >> // Below condition is not true, as all NOT_RUNNING >> // flags were cleared in worker_thread() >> if (worker->flags & WORKER_NOT_RUNNING) >> // Below is true, as worker is running on cpu1 >> if (WARN_ON_ONCE(pool->cpu != raw_smp_processor_id())) >> return NULL; >> // Below is not reached and nr_running stays 1 >> if (atomic_dec_and_test(&pool->nr_running) && >> >> - kworker/0:0 wakes up again, this time on cpu0, as worker->task >> cpus_allowed was set to cpu0, in rebind_workers. >> wq_worker_waking_up() >> if (!(worker->flags & WORKER_NOT_RUNNING)) { >> // Increments pool->nr_running to 2 >> atomic_inc(&worker->pool->nr_running); >> >>>> thread(). >>>> >>>> Worker 0 runs on cpu1 >>>> worker_thread() >>>> process_one_work() >>>> wq_worker_sleeping() >>>> if (worker->flags & WORKER_NOT_RUNNING) >>>> return NULL; >>>> if (WARN_ON_ONCE(pool->cpu != raw_smp_processor_id())) >>>> <Does not decrement nr_running> >>>> >>>> - After this, when kworker/0:0 wakes up, this time on its >>>> bounded cpu cpu0, it increments pool->nr_running again. >>>> So, pool->nr_running becomes 2. >>> Why is it suddenly 2? Who made it one on the account of the kworker? >> As shown in above comment, it became 1 in >> worker_clr_flags(worker, WORKER_PREP | WORKER_REBOUND); >>> >>> Do you see this happening? Or better, is there a (semi) reliable >>> repro for this issue? >> Yes, this was reported in our long run testing with random hotplug. >> Sorry, don't have a quick reproducer for it. Issue is reported in few >> days of testing. >>> >>> Thanks. >>> >> -- >> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a >> member of the Code Aurora Forum, hosted by The Linux Foundation >>
-- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation
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