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Message-ID: <fb854eea-a7e7-b526-a989-95784c1c593c@I-love.SAKURA.ne.jp> Date: Tue, 15 Feb 2022 21:48:58 +0900 From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> To: Haakon Bugge <haakon.bugge@...cle.com> Cc: Tejun Heo <tj@...nel.org>, Bart Van Assche <bvanassche@....org>, syzbot <syzbot+831661966588c802aae9@...kaller.appspotmail.com>, Jason Gunthorpe <jgg@...pe.ca>, LKML <linux-kernel@...r.kernel.org>, OFED mailing list <linux-rdma@...r.kernel.org>, "syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>, Lai Jiangshan <jiangshanlai@...il.com> Subject: Re: [syzbot] possible deadlock in worker_thread On 2022/02/15 19:43, Haakon Bugge wrote: >> @@ -6070,6 +6087,13 @@ void __init workqueue_init_early(void) >> !system_unbound_wq || !system_freezable_wq || >> !system_power_efficient_wq || >> !system_freezable_power_efficient_wq); >> + system_wq->flags |= __WQ_SYSTEM_WIDE; >> + system_highpri_wq->flags |= __WQ_SYSTEM_WIDE; >> + system_long_wq->flags |= __WQ_SYSTEM_WIDE; >> + system_unbound_wq->flags |= __WQ_SYSTEM_WIDE; >> + system_freezable_wq->flags |= __WQ_SYSTEM_WIDE; >> + system_power_efficient_wq->flags |= __WQ_SYSTEM_WIDE; >> + system_freezable_power_efficient_wq->flags |= __WQ_SYSTEM_WIDE; > > Better to OR this in, in the alloc_workqueue() call? Perceive the notion of an opaque object? > I do not want to do like - system_wq = alloc_workqueue("events", 0, 0); + system_wq = alloc_workqueue("events", __WQ_SYSTEM_WIDE, 0); because the intent of this change is to ask developers to create their own WQs. If I pass __WQ_SYSTEM_WIDE to alloc_workqueue(), developers might by error create like srp_tl_err_wq = alloc_workqueue("srp_tl_err_wq", __WQ_SYSTEM_WIDE, 0); because of system_wq = alloc_workqueue("events", __WQ_SYSTEM_WIDE, 0); line. The __WQ_SYSTEM_WIDE is absolutely meant to be applied to only 'system_wq', 'system_highpri_wq', 'system_long_wq', 'system_unbound_wq', 'system_freezable_wq', 'system_power_efficient_wq' and 'system_freezable_power_efficient_wq' WQs, in order to avoid calling flush_workqueue() on these system-wide WQs. I wish I could define __WQ_SYSTEM_WIDE inside kernel/workqueue_internal.h, but it seems that kernel/workqueue_internal.h does not define internal flags.
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