libnvdimm: fix potential deadlock while clearing errors

With the ACPI NFIT 'DSM' methods, acpi can be called from IO paths.
Specifically, the DSM to clear media errors is called during writes, so
that we can provide a writes-fix-errors model.

However it is easy to imagine a scenario like:
 -> write through the nvdimm driver
   -> acpi allocation
     -> writeback, causes more IO through the nvdimm driver
       -> deadlock

Fix this by using memalloc_noio_{save,restore}, which sets the GFP_NOIO
flag for the current scope when issuing commands/IOs that are expected
to clear errors.

Cc: <linux-acpi@vger.kernel.org>
Cc: <linux-nvdimm@lists.01.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Robert Moore <robert.moore@intel.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/bus.c

@@ -11,6 +11,7 @@
  * General Public License for more details.
  */
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+#include <linux/sched/mm.h>
 #include <linux/vmalloc.h>
 #include <linux/uaccess.h>
 #include <linux/module.h>
@@ -234,6 +235,7 @@ long nvdimm_clear_poison(struct device *dev, phys_addr_t phys,
 	struct nd_cmd_clear_error clear_err;
 	struct nd_cmd_ars_cap ars_cap;
 	u32 clear_err_unit, mask;
+	unsigned int noio_flag;
 	int cmd_rc, rc;
 
 	if (!nvdimm_bus)
@@ -250,8 +252,10 @@ long nvdimm_clear_poison(struct device *dev, phys_addr_t phys,
 	memset(&ars_cap, 0, sizeof(ars_cap));
 	ars_cap.address = phys;
 	ars_cap.length = len;
+	noio_flag = memalloc_noio_save();
 	rc = nd_desc->ndctl(nd_desc, NULL, ND_CMD_ARS_CAP, &ars_cap,
 			sizeof(ars_cap), &cmd_rc);
+	memalloc_noio_restore(noio_flag);
 	if (rc < 0)
 		return rc;
 	if (cmd_rc < 0)
@@ -266,8 +270,10 @@ long nvdimm_clear_poison(struct device *dev, phys_addr_t phys,
 	memset(&clear_err, 0, sizeof(clear_err));
 	clear_err.address = phys;
 	clear_err.length = len;
+	noio_flag = memalloc_noio_save();
 	rc = nd_desc->ndctl(nd_desc, NULL, ND_CMD_CLEAR_ERROR, &clear_err,
 			sizeof(clear_err), &cmd_rc);
+	memalloc_noio_restore(noio_flag);
 	if (rc < 0)
 		return rc;
 	if (cmd_rc < 0)