[SRU][B][PATCH 0/2] zpcictl --reset - contribution for kernel (LP: 1870320)

[frank.heimes at canonical.com]

Buglink: https://bugs.launchpad.net/bugs/1870320

SRU Justification:

[Impact]

* With zpci_disable() working, 'lockdep' detected a potential deadlock (in the s390x zPCI subsystem).

* 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.

[Fix]

* Backport 1: https://launchpadlibrarian.net/479554961/0001-s390-pci-Recover-handle-in-clp_set_pci_fn.patch

* Backport 2: https://launchpadlibrarian.net/478714295/0001-s390-pci-Fix-possible-deadlock-in-recover_store.patch

[Test Case]

* It's best to (re-)test using the kernel's locking validator, also known as 'lockdep'.

* Since this potential deadlock was identified by lockdep.

[Regression Potential] 

* The regression potential can be considered as moderate, since:

* It is purely s390x specific code (arch/s390/include/asm/pci.h and arch/s390/pci/{pci.c,pci_clp.c,pci_sysfs.c}).

* It only affects the zPCI, the s390x specific PCI code layer.

* PCI cards available for s390x are optional cards (RoCE and zEDC) and not very wide-spread.

* The states between such a deadlock can happen (recover and power off) are non standard and usually undesired states.

* The patches are upstream accepted since 5.6 and already landed in eoan and focal.

[Other Info]

* Patches 17cdec960cf7 "s390/pci: Recover handle in clp_set_pci_fn()" and 576c75e36c68 "s390/pci: Fix possible deadlock in recover_store()" are upstream accepted since kernel 5.6, but they don't apply cleanly on bionic master-next, hence backports are needed:

* 0001-s390-pci-Recover-handle-in-clp_set_pci_fn.patch is a backport of 17cdec960cf776b20b1fb08c622221babe591d51 17cdec960cf7 "s390/pci: Recover handle in clp_set_pci_fn()"

* 0001-s390-pci-Fix-possible-deadlock-in-recover_store.patch is a backport of 576c75e36c689bec6a940e807bae27291ab0c0de 576c75e36c68 "s390/pci: Fix possible deadlock in recover_store()"

* Both patches/commits already landed in focal (with LP 1863768) and in eoan (with LP 1868324).

Niklas Schnelle (2):
  s390/pci: Recover handle in clp_set_pci_fn()
  s390/pci: Fix possible deadlock in recover_store()

 arch/s390/include/asm/pci.h |  2 +-
 arch/s390/pci/pci.c         |  2 +-
 arch/s390/pci/pci_clp.c     | 46 ++++++++++++++-------------
 arch/s390/pci/pci_sysfs.c   | 63 ++++++++++++++++++++++++-------------
 4 files changed, 69 insertions(+), 44 deletions(-)

-- 
2.25.1