Re: [PATCH AUTOSEL 5.5 094/542] s390/pci: Fix possible deadlock in recover_store()

[Niklas Schnelle]

On Fri, Feb 14, 2020 at 10:41:26AM -0500, Sasha Levin wrote:
> From: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
> 
> [ Upstream commit 576c75e36c689bec6a940e807bae27291ab0c0de ]
> 
> With zpci_disable() working, lockdep detected a potential deadlock
> (lockdep output at the end).
> 
> The deadlock is between recovering a PCI function via the
> 
> /sys/bus/pci/devices/<dev>/recover
> 
> attribute vs powering it off via
> 
> /sys/bus/pci/slots/<slot>/power.
> 
> The fix is analogous to the changes in commit 0ee223b2e1f6 ("scsi: core:
> Avoid that SCSI device removal through sysfs triggers a deadlock")
> that fixed a potential deadlock on removing a SCSI device via sysfs.
[ ... snip ... ]

While technically useful on its own this commit really should go together with
the following upstream commit:

17cdec960cf776b20b1fb08c622221babe591d51
("s390/pci: Recover handle in clp_set_pci_fn()")

While the problem fixed here is independent,  writing to the power/recover
attributes will often fail due to an inconsistent function handle without the
second commit.
In particular without it a PCI function in the error state can not be
recovered or powered off.

I would recommend adding the second commit to the backports as well.

Thanks,
Niklas Schnelle
-- 
Niklas Schnelle
Linux on Z Development