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Date:   Tue, 6 Nov 2018 09:47:52 -0700
From:   Keith Busch <keith.busch@intel.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc:     Bjorn Helgaas <helgaas@kernel.org>,
        Linux PCI <linux-pci@vger.kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Sinan Kaya <okaya@kernel.org>,
        Thomas Tai <thomas.tai@oracle.com>, poza@codeaurora.org,
        Lukas Wunner <lukas@wunner.de>, Christoph Hellwig <hch@lst.de>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/12] error handling and pciehp maintenance
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On Tue, Nov 06, 2018 at 04:34:08PM +0000, Lorenzo Pieralisi wrote:
> The question is whether we really need to dynamically patch the kernel
> with ftrace to achieve what that patch does.
> 
> Furthermore, it would also be good to report what bugs we are actually
> fixing, from what you are writing falling back to the current method if
> !DYNAMIC_FTRACE_WITH_REGS is broken in many ways and I would start with
> fixing the current behaviour with something that does not depend on arch
> features that may not even be implemented.

There are two problems with the current method:

  1. It may dereference pci_dev after it was freed
  2. The pci_dev's children inherit its fake pci_bus's ops on
     enumeration

Both result in kernel panic.

The dynamic kernel patch just seemed like a cool way to inject errors
without messing with the driver's structures. But if there's a more
elegant way to do it, I'm all for it.