Fixes deadlock when closing application with SIGTERM during call of spdk_thread_send_msg. Fixes #1105 Signed-off-by: Kozlowski Mateusz <mateusz.kozlowski@intel.com> Change-Id: If191550f9681a30674fc9c0704289fcdb70b33cb Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/478291 Tested-by: SPDK CI Jenkins <sys_sgci@intel.com> Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com> Reviewed-by: Jim Harris <james.r.harris@intel.com> Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>