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Date: Thu, 14 Jul 2022 07:55:35 +0800 From: Lai Jiangshan <jiangshanlai@...il.com> To: Schspa Shi <schspa@...il.com> Cc: Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>, zhaohui.shi@...izon.ai Subject: Re: [PATCH v2] workqueue: Use active mask for new worker when pool is DISASSOCIATED On Wed, Jul 13, 2022 at 8:51 PM Schspa Shi <schspa@...il.com> wrote: > > When CPU-[un]hotplugs, all workers will be bound to active CPU via > unbind_workers(). > > But the unbound worker still has a chance to create a new worker, which > has bound the newly created task to pool->attrs->cpumask. But the CPU has > been unplugged. > > 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------------- > > And the crash log as fellowing. > > The crash log is as follows: > [ 1622.829074] ------------[ cut here ]------------ > [ 1622.829081] Dying CPU not properly vacated! > [ 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 > [ 1622.829386] Stopper: multi_cpu_stop+0x0/0x160 <- 0x0 > [ 1622.829400] pstate: 60c00009 (nZCv daif +PAN +UAO -TCO BTYPE=--) > [ 1622.829408] pc : sched_cpu_dying+0x74/0x204 > [ 1622.829415] lr : sched_cpu_dying+0x74/0x204 > [ 1622.829421] sp : ffff800012933c70 > [ 1622.829424] pmr_save: 00000060 > [ 1622.829426] x29: ffff800012933c70 x28: 0000000000000000 > [ 1622.829435] x27: 0000000000000000 x26: 0000000000000001 > [ 1622.829444] x25: 0000000000000000 x24: ffff800018353c2c > [ 1622.829452] x23: 0000000000000003 x22: 0000000000000003 > [ 1622.829460] x21: 0000000000000059 x20: 0000000000000000 > [ 1622.829468] x19: ffff00027ee68a80 x18: 0000000000000000 > [ 1622.829477] x17: 0000000000000000 x16: 0000000000000000 > [ 1622.829485] x15: ffffffffffffffff x14: ffff80001169ae30 > [ 1622.829493] x13: ffffffffffc38c07 x12: ffffffffffffffff > [ 1622.829501] x11: ffffffffffe00000 x10: ffff80001169ae58 > [ 1622.829510] x9 : 000000000000001e x8 : ffff80001169ae30 > [ 1622.829518] x7 : ffff800012933ab0 x6 : 00000000ffff0e20 > [ 1622.829526] x5 : ffff00027ee62988 x4 : 00000000ffff0e20 > [ 1622.829535] x3 : ffff800011e30180 x2 : 0000000100000002 > [ 1622.829543] x1 : 0000000000000000 x0 : 0000000000000000 > [ 1622.829552] Call trace: > [ 1622.829555] sched_cpu_dying+0x74/0x204 > [ 1622.829562] cpuhp_invoke_callback+0xc0/0x1b0 > [ 1622.829571] take_cpu_down+0xbc/0xd4 > [ 1622.829577] multi_cpu_stop+0x138/0x160 > [ 1622.829584] cpu_stopper_thread+0x9c/0x118 > [ 1622.829591] smpboot_thread_fn+0x1e8/0x1ec > [ 1622.829598] kthread+0x114/0x124 > [ 1622.829606] ret_from_fork+0x10/0x30 > [ 1622.829615] ---[ end trace 0000000000000002 ]--- > [ 1623.830273] CPU3 enqueued tasks (2 total): > [ 1623.830291] pid: 31, name: migration/3 > [ 1623.830440] pid: 25654, name: kworker/3:0 > [ 1623.830444] task:kworker/3:0 state:R running task stack: 0 pid:25654 ppid: 2 flags:0x00000028 > [ 1623.830458] Call trace: > [ 1623.830460] __switch_to+0x164/0x17c > [ 1623.830472] __schedule+0x4cc/0x5c0 > [ 1623.830483] schedule+0x7c/0xcc > [ 1623.830491] schedule_preempt_disabled+0x14/0x24 > [ 1623.830500] kthread+0xd8/0x124 > [ 1623.830509] ret_from_fork+0x10/0x30 > > In the crash log, the error enqueued kworker(pid: 25654, name: kworker/3:0) > is a newly created thread, and have bind to a unpluged CPU 3. > > Can crash dump can also verify this. > crash> task -R nr_cpus_allowed,cpus_mask 25654 > PID: 25654 TASK: ffff000181ff0000 CPU: 3 COMMAND: "kworker/3:0" > nr_cpus_allowed = 1, > cpus_mask = { > bits = {8, 0} > }, > > crash> struct worker_pool.cpu,nr_workers,attrs 0xffff00027ee68380 > cpu = 3, > nr_workers = 3, > attrs = 0xffff000180004480, > crash> struct workqueue_attrs 0xffff000180004480 > struct workqueue_attrs { > nice = 0, > cpumask = {{ > bits = {8, 0} > }}, > no_numa = false > } > > The stack trace of the bad running task was dumped via the following patch: > Link: https://lore.kernel.org/all/20220519161125.41144-1-schspa@gmail.com/ > And I think this debug patch needs to be added to the mainline, > it can help us to debug this kind of problem > > To fix it, we can use cpu_active_mask when work pool is DISASSOCIATED. > > Signed-off-by: Schspa Shi <schspa@...il.com> > > -- > > Changelog: > v1 -> v2: > - Move worker task bind to worker_attach_to_pool, remove extra > wq_pool_attach_mutex added. > - Add a timing diagram to make this question clearer. > --- > kernel/workqueue.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index 1ea50f6be843..3f6e6d884793 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -1867,13 +1867,13 @@ static void worker_attach_to_pool(struct worker *worker, > * stable across this function. See the comments above the flag > * definition for details. > */ > - if (pool->flags & POOL_DISASSOCIATED) > + if (pool->flags & POOL_DISASSOCIATED) { > worker->flags |= WORKER_UNBOUND; > - else > + set_cpus_allowed_ptr(worker->task, cpu_active_mask); > + } else { > kthread_set_per_cpu(worker->task, pool->cpu); > - > - if (worker->rescue_wq) > set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask); > + } For unbound pools (get_unbound_pool(), which also has POOL_DISASSOCIATED), pool->attrs->cpumask should be used if pool->attrs->cpumask has active cpu. if (cpumask_intersects(pool->attrs->cpumask, cpu_active_mask)) set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask); else set_cpus_allowed_ptr(worker->task, wq_unbound_cpumask); And put it above the "if (pool->flags & POOL_DISASSOCIATED)" code block. > > list_add_tail(&worker->node, &pool->workers); > worker->pool = pool; > @@ -1952,7 +1952,6 @@ static struct worker *create_worker(struct worker_pool *pool) > goto fail; > > set_user_nice(worker->task, pool->attrs->nice); > - kthread_bind_mask(worker->task, pool->attrs->cpumask); worker->flags |= PF_NO_SETAFFINITY; PF_NO_SETAFFINITY needs to be set for workers. > > /* successful, attach the worker to the pool */ > worker_attach_to_pool(worker, pool); > -- > 2.29.0 >
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