On Fri, Sep 27, 2019 at 02:45:10PM +0200, Frederic Barrat wrote: > Recent cleanup in the way EEH support is added to a device causes a > kernel oops when the cxl driver probes a device and creates virtual > devices discovered on the FPGA: > > BUG: Kernel NULL pointer dereference at 0x000000a0 > Faulting instruction address: 0xc000000000048070 > Oops: Kernel access of bad area, sig: 7 [#1] > ... > NIP [c000000000048070] eeh_add_device_late.part.9+0x50/0x1e0 > LR [c00000000004805c] eeh_add_device_late.part.9+0x3c/0x1e0 > Call Trace: > [c000200e43983900] [c00000000079e250] _dev_info+0x5c/0x6c (unreliable) > [c000200e43983980] [c0000000000d1ad0] pnv_pcibios_bus_add_device+0x60/0xb0 > [c000200e439839f0] [c0000000000606d0] pcibios_bus_add_device+0x40/0x60 > [c000200e43983a10] [c0000000006aa3a0] pci_bus_add_device+0x30/0x100 > [c000200e43983a80] [c0000000006aa4d4] pci_bus_add_devices+0x64/0xd0 > [c000200e43983ac0] [c00800001c429118] cxl_pci_vphb_add+0xe0/0x130 [cxl] > [c000200e43983b00] [c00800001c4242ac] cxl_probe+0x504/0x5b0 [cxl] > [c000200e43983bb0] [c0000000006bba1c] local_pci_probe+0x6c/0x110 > [c000200e43983c30] [c000000000159278] work_for_cpu_fn+0x38/0x60 > > The root cause is that those cxl virtual devices don't have a > representation in the device tree and therefore no associated pci_dn > structure. In eeh_add_device_late(), pdn is NULL, so edev is NULL and > we oops. > > We never had explicit support for EEH for those virtual > devices. Instead, EEH events are reported to the (real) pci device and > handled by the cxl driver. Which can then forward to the virtual > devices and handle dependencies. The fact that we try adding EEH > support for the virtual devices is new and a side-effect of the recent > cleanup. > > This patch fixes it by skipping adding EEH support on powernv for > devices which don't have a pci_dn structure. > > Fixes: b905f8cdca77 ("powerpc/eeh: EEH for pSeries hot plug") > Signed-off-by: Frederic Barrat <fbar...@linux.ibm.com> > --- > > Sending as an RFC, as I'm afraid of hiding potential issues and would > be interested in comments. The powernv eeh code expects a struct > pci_dn, so the fix seems safe. I'm wondering if there could be cases > (other than capi virtual devices) where we'd want to blow up and fix > instead of going undetected with this patch.
Looks good to me. I do think it would be good to detect a missing pci_dn (WARN_ONCE() might be appropriate). However to implement it, pnv_pcibios_bus_add_device() would need a way to detect that a struct pci_dev is a cxl virtual device. I don't see an easy way to do that; do you know if it's possible? One last thing: pseries_pcibios_bus_add_device() also requires a pci_dn. Do you know if it's possible to trigger a similar issue there, or is it not possible for some reason? Cheers, Sam. > arch/powerpc/platforms/powernv/eeh-powernv.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/powerpc/platforms/powernv/eeh-powernv.c > b/arch/powerpc/platforms/powernv/eeh-powernv.c > index 6bc24a47e9ef..6f300ab7f0e9 100644 > --- a/arch/powerpc/platforms/powernv/eeh-powernv.c > +++ b/arch/powerpc/platforms/powernv/eeh-powernv.c > @@ -42,7 +42,7 @@ void pnv_pcibios_bus_add_device(struct pci_dev *pdev) > { > struct pci_dn *pdn = pci_get_pdn(pdev); > > - if (eeh_has_flag(EEH_FORCE_DISABLED)) > + if (!pdn || eeh_has_flag(EEH_FORCE_DISABLED)) > return; > > dev_dbg(&pdev->dev, "EEH: Setting up device\n"); > -- > 2.21.0 >
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