[SRU][Bionic][PATCH 0/1] Fixes for LP1800849
frank.heimes at canonical.com
Thu Nov 1 15:26:26 UTC 2018
== SRU Justification ==
Description: kvm: fix deadlock when killed by oom
Symptom: oom killer leaves processes in a deadlock state.
Problem: The problem arises in the rare cases in which
handle_mm_fault does not release the mm_sem.
Solution: Correct the issue by manually release the mm_sem when needed.
== Fix ==
306d6c49ac9ded11114cb53b0925da52f2c2ada1 ("s390/kvm: fix deadlock when
killed by oom")
== Patch ==
Author: Claudio Imbrenda <imbrenda at linux.vnet.ibm.com>
Date: Mon Jul 16 10:38:57 2018 +0200
s390/kvm: fix deadlock when killed by oom
When the oom killer kills a userspace process in the page fault handler
while in guest context, the fault handler fails to release the mm_sem
if the FAULT_FLAG_RETRY_NOWAIT option is set. This leads to a deadlock
when tearing down the mm when the process terminates. This bug can only
happen when pfault is enabled, so only KVM clients are affected.
The problem arises in the rare cases in which handle_mm_fault does not
release the mm_sem. This patch fixes the issue by manually releasing
the mm_sem when needed.
Fixes: 24eb3a824c4f3 ("KVM: s390: Add FAULT_FLAG_RETRY_NOWAIT for guest
Cc: <stable at vger.kernel.org> # 3.15+
Signed-off-by: Claudio Imbrenda <imbrenda at linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky at de.ibm.com>
== Regression Potential ==
Low and minimal, because:
- code change is s390x only
- limited to one single file: /arch/s390/mm/fault.c
- just two additional lines added (if stmt)
- Xenial and Cosmic already have this commit via upstream stable updates.
- Hence patch is just missing in Bionic.
- Test kernel was made available.
== Test Case ==
Create numerous KVM guests so that the host starts swapping
and memory becomes overcomitted and the oom killer is triggered.
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