Re: [PATCH RT] nvdimm: make lane acquirement RT aware

Currently, nvdimm driver isn't RT compatible. nd_region_acquire_lane() disables preemption with get_cpu() which causes "scheduling while atomic" spews on RT, when using fio to test pmem as block device. In this change, we replace get_cpu/put_cpu with local_lock_cpu/ local_unlock_cpu, and introduce per CPU variable "ndl_local_lock". Due to preemption on RT, this lock can avoid race condition for the same lane on the same CPU. When CPU number is greater than the lane number, lane can be shared among CPUs. "ndl_lock->lock" is used to protect the lane in this situation. This patch is derived from Dan Williams and Pankaj Gupta's proposal from https://www.mail-archive.com/linux-nvdimm@lists.01.org/msg13359.html and https://www.spinics.net/lists/linux-rt-users/msg20280.html. Many thanks to them. Cc: Dan Williams <dan.j.williams(a)intel.com&gt; Cc: Pankaj Gupta <pagupta(a)redhat.com&gt; Cc: linux-rt-users <linux-rt-users(a)vger.kernel.org&gt; Cc: linux-nvdimm <linux-nvdimm(a)lists.01.org&gt; Signed-off-by: Yongxin Liu <yongxin.liu(a)windriver.com&gt;