** Description changed:
+ == 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 ==
+
+ commit 306d6c49ac9ded11114cb53b0925da52f2c2ada1
+ Author: Claudio Imbrenda <[email protected]>
+ 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
fault")
+ Cc: <[email protected]> # 3.15+
+ Signed-off-by: Claudio Imbrenda <[email protected]>
+ Signed-off-by: Martin Schwidefsky <[email protected]>
+
+ == 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 build for testting.
+
+ == Test Case ==
+
+ Create numerous KVM guests so that the host starts swapping
+ and memory becomes overcomitted and the oom killer is triggered.
+ __________
+
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.
+ handle_mm_fault does not release the mm_sem.
Solution: Correct the issue by manually relaese the mm_sem
- when needed.
+ when needed.
Reproduction: Create numerous KVM guests so that the host starts
- swapping and memory becomes overcomitted and the oom
- killer is triggered.
-
+ swapping and memory becomes overcomitted and the oom
+ killer is triggered.
kernel 4.19
Upstream-ID: 306d6c49ac9ded11114cb53b0925da52f2c2ada1
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https://bugs.launchpad.net/bugs/1800849
Title:
[Ubuntu] kvm: fix deadlock when killed by oom
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