4.4-stable review patch. If anyone has any objections, please let me know.
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From: Claudio Imbrenda imbrenda@linux.vnet.ibm.com
commit 306d6c49ac9ded11114cb53b0925da52f2c2ada1 upstream.
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: 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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/s390/mm/fault.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/arch/s390/mm/fault.c +++ b/arch/s390/mm/fault.c @@ -459,6 +459,8 @@ 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))