linux-kernel - Re: [PATCH v3 2/2] PCI: pciehp: Prevent deadlock on disconnect

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Date:   Wed, 13 Nov 2019 07:35:19 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Keith Busch <keith.busch@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Frederick Lawler <fred@...dlawl.com>,
        "Gustavo A . R . Silva" <gustavo@...eddedor.com>,
        Sinan Kaya <okaya@...nel.org>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] PCI: pciehp: Prevent deadlock on disconnect

On Tue, Nov 12, 2019 at 09:17:52PM -0600, Bjorn Helgaas wrote:
> On Tue, Oct 29, 2019 at 08:00:22PM +0300, Mika Westerberg wrote:
> > parent PCIe downstream port, who got the hot-remove event, starts
> > removing devices below it taking pci_lock_rescan_remove() lock. When the
> > child PCIe port is runtime resumed it calls pciehp_check_presence()
> > which ends up calling pciehp_card_present() and pciehp_check_link_active().
> 
> Oh, I see, pciehp_resume() calls pciehp_check_presence(), which
> schedules the IRQ thread via pciehp_request().  So does this deadlock
> only happen if the port(s) have been runtime suspended?

No, there is a multitude of situations when the deadlock may occur and
this is just one of them.  See my comment on v1 of this patch:

https://patchwork.ozlabs.org/patch/1117870/#2230798

Thanks,

Lukas