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Date: Tue, 8 Jan 2013 11:11:24 -0700 From: Bjorn Helgaas <bhelgaas@...gle.com> To: Yijing Wang <wangyijing@...wei.com> Cc: Jiang Liu <liuj97@...il.com>, Daniel J Blueman <daniel@...ra.org>, Jesse Barnes <jbarnes@...tuousgeek.org>, Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>, Yinghai Lu <yinghai@...nel.org>, Linux Kernel <linux-kernel@...r.kernel.org>, Linux PCI <linux-pci@...r.kernel.org> Subject: Re: 3.8-rc2: pciehp waitqueue hang... On Sun, Jan 6, 2013 at 5:13 AM, Yijing Wang <wangyijing@...wei.com> wrote: > On 2013/1/5 5:50, Bjorn Helgaas wrote: >> [+to Yijing, +cc Kenji] >> >> On Fri, Jan 4, 2013 at 1:01 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote: >>> On Thu, Jan 3, 2013 at 8:41 AM, Jiang Liu <liuj97@...il.com> wrote: >>>> Hi Daniel, >>>> It seems like an issue caused by recursive PCIe HPC. >>>> Could you please help to try the patch from: >>>> http://www.spinics.net/lists/linux-pci/msg18625.html >>> >>> Hi Gerry, >>> >>> I'm working on merging this patch. Seems like something that might be >>> appropriate for stable as well. >>> >>> Did you look for similar problems in other hotplug drivers? >> >> Oops, sorry, I forgot that Yijing is the author of the patch in question. >> >> Yijing, please check for the same problem in other hotplug drivers. >> Questions I have after a quick look: >> > > Hi Bjorn, > Sorry for delay reply. There are some busy work these days. > >> - shpchp_wq looks like it might have the same deadlock issue. > > shpchp driver uses two workqueues shpchp_wq and shpchp_ordered_wq, they are created by alloc_ordered_workqueue > which set the "max_active" parameter to 1. So only one pci hotplug slot can do hotplug at the same time. > shpchp introduced these workqueue to remove the use of flush_scheduled_work() which is deprecated and scheduled for removal. > > hot remove path is: > button press > shpc_isr(interrupt handler) > shpchp_handle_attention_button > queue_interrupt_event > queue_work "interrupt_event_handler" into "shpchp_wq" > interrupt_event_handler > handle_button_press_event > queue_delayed_work "shpchp_queue_pushbutton_work" into "shpchp_wq" > queue_work "shpchp_pushbutton_thread" into "shpchp_ordered_wq" > shpchp_pushbutton_thread > shpchp_disable_slot > pci_stop_and_remove_bus_device > ...... > shpc_remove() if the hotplug slot connected a iobox which contains some hotplug pcieport, shpc_remove will be called when remove pcie port device. > hpc_release_ctlr > flush_workqueue(shpchp_wq); > flush_workqueue(shpchp_ordered_wq); > So hotplug task hang. > shpchp driver has the same deadlock issue like pciehp driver, I think we should fix the issue, I will send out the patch if you agree this, but I have no machine support shpchp hotplug, > so I can't test this patch in real machine. That's OK. You've tested pciehp, and I don't want to leave shpchp broken the same way just because we can't test a similar fix there, so please do send the shpchp patch, too. >> - pciehp_wq (and your per-slot replacement) are allocated with >> alloc_workqueue(). shpchp_wq is allocated with >> alloc_ordered_workqueue(). Why the difference? > > alloc_workqueue(name, 0, 0) set max_active to 0(0 is default value used and support 256 work items of the wq can be executing at the same time per CPU). > So pciehp driver can handle push button event asynchronously. > > alloc_ordered_workqueue can only one handle push button event at the same time. pciehp and shpchp should work the same in this respect unless there's a reason they can't, so it sounds like we should make shpchp work like pciehp. >> - The alloc/alloc_ordered difference might be related to 486b10b9f4, >> where Kenji removed alloc_ordered from pciehp. Should a similar >> change be made to shpchp? > > Yes, I agree, we can use per-slot workqueue to fix this issue. > >> >> - acpiphp uses the global kacpi_hotplug_wq. We never flush or drain >> kacpi_hotplug_wq, so I doubt there's a deadlock issue, but I wonder if >> there are any ordering issues there because we *don't* ever wait for >> things in that queue to be completed. > > acpiphp driver is not attach to a pci device, so when hot remove pci device, driver will not to flush or drain kacpi_hotplug_wq. > But if we do acpiphp hot remove in sequence like this, there maybe cause some unexpected errors, I think. > slot(A)------pcie port----slot(B) > slot A and slot B both support acpiphp hotplug. > 1、press attention button on slot A; > 2、press attention button on slot B quickly after step 1; > Because kacpi_hotplug_wq is a ordered workqueue, slot B hot remove won't run unless slot A hot remove action completed. > After Slot B hot remove completed, some resources of slot A also has been destroyed. So slot B hot remove will cause some unexpected errors. > Because my hotplug machine's bios don't support iobox hotplug(slot-connected-slot), I can't verify this situation. Hmm. That definitely sounds like a potential problem. But I think it's beyond the scope of the issue you're trying to fix, and any fix would look much different from your current pciehp patch, so I think we can treat it separately. Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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