** Changed in: linux (Ubuntu Plucky)
Status: In Progress => Fix Committed
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https://bugs.launchpad.net/bugs/2121149
Title:
[UBUNTU 24.04] s390/pci: Fix stale function handles in error handling
Status in Ubuntu on IBM z Systems:
In Progress
Status in linux package in Ubuntu:
Invalid
Status in linux source package in Noble:
Fix Committed
Status in linux source package in Plucky:
Fix Committed
Bug description:
[ Impact ]
s390/pci: Fix stale function handles in error handling
In some error scenarios multiple error events may be generated for the
same PCI function before Linux even started its automatic recovery
process. In this case Linux may succeed to recover based on the first
event but then fails recovery when handling a subsequent event. This
is because events capture the function handle as they are created. At
the time when the secondary event is handled the handle stored with
the error event is then stale and using it to reset the function will
fail.
Fix this by retrieving a fresh function handle using the CLP List PCI
Functions and only process events where the stored handle matches this
handle. This effectively ignores error events which were captured
before the latest disable/enable cycles. Relatedly if the current
handle is already disabled do not attempt to simply reset the error
state as a re-enable is necessary and clearing the error state would
fail.
[ Fix ]
Backport the following commits from upstream:
- 45537926dd2a s390/pci: Fix stale function handles in error handling
- b97a7972b1f4 s390/pci: Do not try re-enabling load/store if device is
disabled
[ Test Plan ]
Booting the system on a IBM Z mainframe with at least one PCI passthrough
device available.
Enable debug logging in order to monitor how error events are processed in
real time.
Trigger PCI error conditions, either through firmware error injection or by
repeatedly disabling and re-enabling the device under load using sysfs
interfaces.
While the device is busy handling real traffic, such as network or crypto
operations, watch the kernel logs to see how error events are processed.
Verify that events carrying stale function handles are detected and ignored,
and that recovery attempts against disabled devices escalate properly to a full
reset.
[ Regression Potential ]
The fix affects how the s390 PCI error handler validates and uses function
handles during recovery.
A bug here could cause valid error events to be incorrectly ignored or
recovery paths to escalate unnecessarily.
Users may see PCI devices not recovering from transient errors, devices being
reset or re-enabled more often than required, or even unexpected device removal.
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Description: s390/pci: Fix stale function handles in error handling
Symptom:
In some error scenarios automatic recovery may ultimately fail after Linux
initially recovered successfully when it then tries to handle another error
event.
Problem:
In some error scenarios multiple error events may be generated for the same
PCI function before Linux even started its automatic recovery process. In this
case Linux may succeed to recover based on the first event but then fails
recovery when handling a subsequent event. This is because events capture the
function handle as they are created. At the time when the secondary event is
handled the handle stored with the error event is then stale and using it to
reset the function will fail.
Solution:
Fix this by retrieving a fresh function handle using the CLP List PCI
Functions and only process events where the stored handle matches this handle.
This effectively ignores error events which were captured before the latest
disable/enable cycles. Relatedly if the current handle is already disabled do
not attempt to simply reset the error state as a re-enable is necessary and
clearing the error state would fail.
Reproduction:
This may be reproduced in an artificial error scenario by issuing multiple
zpcictl --reset-fw <dev> in quick succession generating multiple PEC 0x3A
events with the same handle.
Required Fixes / Upstream-IDs:
45537926dd2aaa9190ac0fac5a0fbeefcadfea95
b97a7972b1f4f81417840b9a2ab0c19722b577d5
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