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From: Lukas Wunner <lukas@wunner.de>
To: Ethan Zhao <xerces.zhao@gmail.com>
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>
Subject: Re: [PATCH 2/5 V2] PCI: pciehp: check and wait port status out of DPC before handling DLLSC and PDC
Date: Tue, 29 Sep 2020 12:07:59 +0200	[thread overview]
Message-ID: <20200929100759.GA21885@wunner.de> (raw)
In-Reply-To: <CAKF3qh3UxkVOwCOUB4rNdxLX0k9oZQRzXT_N0BNYKWL_BAHa5w@mail.gmail.com>

On Tue, Sep 29, 2020 at 05:46:41PM +0800, Ethan Zhao wrote:
> 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.
[...]
> > > 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.

Please reorder the series to fix the null pointer deref first,
i.e. move patch 3 before patch 2.  If the null pointer deref is
fixed by patch 3, do not mention it in patch 2.

Thanks,

Lukas

  reply	other threads:[~2020-09-29 10:15 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-27  3:28 [PATCH 0/5 V2] Fix DPC hotplug race and enhance error handling Ethan Zhao
2020-09-27  3:28 ` [PATCH 1/5 V2] PCI: define a function to check and wait till port finish DPC handling Ethan Zhao
2020-09-27  6:23   ` Christoph Hellwig
2020-09-27  6:43     ` Zhao, Haifeng
2020-09-29  2:32     ` Ethan Zhao
2020-09-27  3:28 ` [PATCH 2/5 V2] PCI: pciehp: check and wait port status out of DPC before handling DLLSC and PDC Ethan Zhao
2020-09-27 15:27   ` Sinan Kaya
2020-09-28  2:01     ` Zhao, Haifeng
2020-09-28 11:10       ` Sinan Kaya
2020-09-28 16:43         ` Sinan Kaya
2020-09-28 16:44           ` Kuppuswamy, Sathyanarayanan
2020-09-29  2:28             ` Ethan Zhao
2020-09-29  2:50           ` Ethan Zhao
2020-09-29  8:18     ` Lukas Wunner
2020-09-29  9:46       ` Ethan Zhao
2020-09-29 10:07         ` Lukas Wunner [this message]
2020-09-30  2:20           ` Ethan Zhao
2020-09-27  3:28 ` [PATCH 3/5 V2] PCI/ERR: get device before call device driver to avoid NULL pointer reference Ethan Zhao
2020-09-27  3:28 ` [PATCH 4/5 V2] PCI: only return true when dev io state is really changed Ethan Zhao
2020-09-27  4:16   ` Joe Perches
2020-09-27  5:12     ` Zhao, Haifeng
2020-09-27  3:28 ` [PATCH 5/5 V2] PCI/ERR: don't mix io state not changed and no driver together Ethan Zhao

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