Re: [PATCH v2 1/1] powerpc/eeh: fix recursive pci_lock_rescan_remove locking in EEH event handling

[Narayana Murty N]

On 11/12/25 9:15 PM, Timothy Pearson wrote:
> ----- Original Message -----
> > From: "Narayana Murty N" <nnmlinux@xxxxxxxxxxxxx>
> > To: "mahesh" <mahesh@xxxxxxxxxxxxx>, "Oliver" <oohall@xxxxxxxxx>, "Madhavan Srinivasan" <maddy@xxxxxxxxxxxxx>, "Michael
> > Ellerman" <mpe@xxxxxxxxxxxxxx>, "npiggin" <npiggin@xxxxxxxxx>, "christophe leroy" <christophe.leroy@xxxxxxxxxx>
> > Cc: "Bjorn Helgaas" <bhelgaas@xxxxxxxxxx>, "Timothy Pearson" <tpearson@xxxxxxxxxxxxxxxxxxxxx>, "linuxppc-dev"
> > <linuxppc-dev@xxxxxxxxxxxxxxxx>, "linux-kernel" <linux-kernel@xxxxxxxxxxxxxxx>, "vaibhav" <vaibhav@xxxxxxxxxxxxx>,
> > "Shivaprasad G Bhat" <sbhat@xxxxxxxxxxxxx>, ganeshgr@xxxxxxxxxxxxx
> > Sent: Wednesday, December 10, 2025 8:25:59 AM
> > Subject: [PATCH v2 1/1] powerpc/eeh: fix recursive pci_lock_rescan_remove locking in EEH event handling
> > The recent commit 1010b4c012b0 ("powerpc/eeh: Make EEH driver device
> > hotplug safe") restructured the EEH driver to improve synchronization
> > with the PCI hotplug layer.
> >
> > However, it inadvertently moved pci_lock_rescan_remove() outside its
> > intended scope in eeh_handle_normal_event(), leading to broken PCI
> > error reporting and improper EEH event triggering. Specifically,
> > eeh_handle_normal_event() acquired pci_lock_rescan_remove() before
> > calling eeh_pe_bus_get(), but eeh_pe_bus_get() itself attempts to
> > acquire the same lock internally, causing nested locking and disrupting
> > normal EEH event handling paths.
> >
> > This patch adds a boolean parameter do_lock to _eeh_pe_bus_get(),
> > with two public wrappers:
> >     eeh_pe_bus_get() with locking enabled.
> >     eeh_pe_bus_get_nolock() that skips locking.
> >
> > Callers that already hold pci_lock_rescan_remove() now use
> > eeh_pe_bus_get_nolock() to avoid recursive lock acquisition.
> >
> > Additionally, pci_lock_rescan_remove() calls are restored to the correct
> > position—after eeh_pe_bus_get() and immediately before iterating affected
> > PEs and devices. This ensures EEH-triggered PCI removes occur under proper
> > bus rescan locking without recursive lock contention.
> >
> > The eeh_pe_loc_get() function has been split into two functions:
> >     eeh_pe_loc_get(struct eeh_pe *pe) which retrieves the loc for given PE.
> >     eeh_pe_loc_get_bus(struct pci_bus *bus) which retrieves the location
> >     code for given bus.
> Conceptually the patch sounds OK, but given the complexity of these subsystems it's difficult to forsee all interactions.  Was the patch verified not to break NVMe hotplug on PowerNV systems using actual hardware?  If not, I will need to do so before sending an ack.  Thanks!
It has not been specifically tested for NVMe hotplug on PowerNV hardware.

However, this change does not remove or relax any of the existing locking

around EEH handling, so the NVMe hotplug paths should continue to see

the same serialization as before.

If you have a convenient setup for NVMe hotplug on PowerNV, additional 
testing

there would definitely be helpful before merging.

Thanks,
Narayana Murty