Commit 306d6c49 authored Jul 16, 2018 by Claudio Imbrenda Committed by Martin Schwidefsky Jul 16, 2018

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: 24eb3a82 ("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>

parent ac4c4fc8

arch/s390/mm/fault.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -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))

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