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In-Reply-To: <20200929081800.GA15858@wunner.de>
From:   Ethan Zhao <xerces.zhao@gmail.com>
Date:   Tue, 29 Sep 2020 17:46:41 +0800
Message-ID: <CAKF3qh3UxkVOwCOUB4rNdxLX0k9oZQRzXT_N0BNYKWL_BAHa5w@mail.gmail.com>
Subject: Re: [PATCH 2/5 V2] PCI: pciehp: check and wait port status out of DPC
 before handling DLLSC and PDC
To:     Lukas Wunner <lukas@wunner.de>
Cc:     Sinan Kaya <okaya@kernel.org>, Ethan Zhao <haifeng.zhao@intel.com>,
        Bjorn Helgaas <bhelgaas@google.com>, Oliver <oohall@gmail.com>,
        ruscur@russell.cc,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Stuart Hayes <stuart.w.hayes@gmail.com>,
        Alexandru Gagniuc <mr.nuke.me@gmail.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Keith Busch <keith.busch@intel.com>,
        linux-pci <linux-pci@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Jia, Pei P" <pei.p.jia@intel.com>, ashok.raj@linux.intel.com,
        Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@intel.com>
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On Tue, Sep 29, 2020 at 4:29 PM Lukas Wunner <lukas@wunner.de> wrote:
>
> On Sun, Sep 27, 2020 at 11:27:46AM -0400, Sinan Kaya wrote:
> > On 9/26/2020 11:28 PM, Ethan Zhao wrote:
> > > --- a/drivers/pci/hotplug/pciehp_hpc.c
> > > +++ b/drivers/pci/hotplug/pciehp_hpc.c
> > > @@ -710,8 +710,10 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id)
> > >     down_read(&ctrl->reset_lock);
> > >     if (events & DISABLE_SLOT)
> > >             pciehp_handle_disable_request(ctrl);
> > > -   else if (events & (PCI_EXP_SLTSTA_PDC | PCI_EXP_SLTSTA_DLLSC))
> > > +   else if (events & (PCI_EXP_SLTSTA_PDC | PCI_EXP_SLTSTA_DLLSC)) {
> > > +           pci_wait_port_outdpc(pdev);
> > >             pciehp_handle_presence_or_link_change(ctrl, events);
> > > +   }
> > >     up_read(&ctrl->reset_lock);
> >
> > This looks like a hack TBH.
> >
> > Lukas, Keith;
> >
> > What is your take on this?
> > Why is device lock not protecting this situation?
> >
> > Is there a lock missing in hotplug driver?
>
> According to Ethan's commit message, there are two issues here:
> One, that pciehp may remove a device even though DPC recovered the error,
> and two, that a null pointer deref occurs.
>
> The latter is most certainly not a locking issue but failure of DPC
> to hold a reference on the pci_dev.

This is what patch 3/5 proposed to fix. while this one is to re-order
the mixed DPC
recovery procedure and DLLSC/PDC event handling, to make pciehp to know the
exact recovered result of DPC to malfunctional device ---- link
recovered, still there,
or is removed from the slot.

Thanks,
Ethan

>
> Thanks,
>
> Lukas