linux-kernel - Re: [PATCH v2 2/2] PCI: pciehp: Prevent deadlock on disconnect

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Message-Id: <0DDD8724-5331-495C-BB20-3754B1E667D3@canonical.com>
Date:   Fri, 18 Oct 2019 15:10:32 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     AceLan Kao <acelan.kao@...onical.com>,
        Lukas Wunner <lukas@...ner.de>,
        Bjorn Helgaas <bhelgaas@...gle.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>,
        Linux PCI <linux-pci@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] PCI: pciehp: Prevent deadlock on disconnect

Hi Mika,

> On Sep 23, 2019, at 16:28, Mika Westerberg <mika.westerberg@...ux.intel.com> wrote:
> 
> On Mon, Sep 23, 2019 at 11:12:42AM +0300, Mika Westerberg wrote:
>> Regarding suggestion of unbinding PCI drivers without
>> pci_lock_rescan_remove() hold, I haven't looked it too closely but I
>> think we need to take that lock anyway because when we are unbinding a
>> hotplug driver it is supposed to remove the hierarchy below touching the
>> shared structures, possibly concurrently. Unfortunately there is no
>> documentation what data pci_lock_rescan_remove() actually protects so
>> first one needs to understand that. I think one way to clean up this is
>> to use finer grained locking (with documented lock ordering) for PCI bus
>> structures that can be accessed simultaneusly by different threads. But
>> that is not a simple task.
> 
> Now that I looked more closely, I realized it actually is not supposed
> to remove the hierarchy below so indeed it might be possible to do that
> without taking pci_lock_rescan_remove().

This series fixes S3 resume hang when native PCIe TBT is connected to TBT dock.
Is there going to be a v3 of this series?

Anyway, please collect my tested-by tag,
Tested-by: Kai-Heng Feng <kai.heng.feng@...onical.com>

Kai-Heng