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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: 24eb3a824c ("KVM: s390: Add FAULT_FLAG_RETRY_NOWAIT for guest fault")
Cc: <stable@vger.kernel.org> # 3.15+
Signed-off-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Claudio Imbrenda 2018-07-16 10:38:57 +02:00 committed by Martin Schwidefsky
parent ac4c4fc87d
commit 306d6c49ac
1 changed files with 2 additions and 0 deletions
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2
arch/s390/mm/fault.c
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@ -502,6 +502,8 @@ retry:
/* No reason to continue if interrupted by SIGKILL. */
if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
fault = VM_FAULT_SIGNAL;
if (flags & FAULT_FLAG_RETRY_NOWAIT)
goto out_up;
goto out;
}
if (unlikely(fault & VM_FAULT_ERROR))