From: Vishal Verma <vishal.l.verma@intel.com>
Date: Wed, 30 Aug 2017 19:36:02 -0600
Subject: libnvdimm: fix potential deadlock while clearing errors
Patch-mainline: v4.14-rc1
Git-commit: 0930a750c35be3c2f5aacebc0d20ddeaf727c208
References: FATE#323731

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>
Acked-by: Johannes Thumshirn <jthumshirn@suse.de>
---
 drivers/nvdimm/bus.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/nvdimm/bus.c
+++ b/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>
@@ -231,6 +232,7 @@ long nvdimm_clear_poison(struct device *
 	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)
@@ -247,8 +249,10 @@ long nvdimm_clear_poison(struct device *
 	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)
@@ -263,8 +267,10 @@ long nvdimm_clear_poison(struct device *
 	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)