[PATCHv2 2/3] i915: convert to new mount API

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

tmpfs does not set ->remount_fs() anymore and its users need
to be converted to new mount API.

 BUG: kernel NULL pointer dereference, address: 0000000000000000
 PF: supervisor instruction fetch in kernel mode
 PF: error_code(0x0010) - not-present page
 RIP: 0010:0x0
 Code: Bad RIP value.
 Call Trace:
  i915_gemfs_init+0x6e/0xa0 [i915]
  i915_gem_init_early+0x76/0x90 [i915]
  i915_driver_probe+0x30a/0x1640 [i915]
  ? kernfs_activate+0x5a/0x80
  ? kernfs_add_one+0xdd/0x130
  pci_device_probe+0x9e/0x110
  really_probe+0xce/0x230
  driver_probe_device+0x4b/0xc0
  device_driver_attach+0x4e/0x60
  __driver_attach+0x47/0xb0
  ? device_driver_attach+0x60/0x60
  bus_for_each_dev+0x61/0x90
  bus_add_driver+0x167/0x1b0
  driver_register+0x67/0xaa

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gem/i915_gemfs.c | 32 +++++++++++++++++++--------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gemfs.c b/drivers/gpu/drm/i915/gem/i915_gemfs.c
index 099f3397aada..feedc9242072 100644
--- a/drivers/gpu/drm/i915/gem/i915_gemfs.c
+++ b/drivers/gpu/drm/i915/gem/i915_gemfs.c
@@ -7,14 +7,17 @@
 #include <linux/fs.h>
 #include <linux/mount.h>
 #include <linux/pagemap.h>
+#include <linux/fs_context.h>
 
 #include "i915_drv.h"
 #include "i915_gemfs.h"
 
 int i915_gemfs_init(struct drm_i915_private *i915)
 {
+	struct fs_context *fc = NULL;
 	struct file_system_type *type;
 	struct vfsmount *gemfs;
+	bool ok = true;
 
 	type = get_fs_type("tmpfs");
 	if (!type)
@@ -36,18 +39,29 @@ int i915_gemfs_init(struct drm_i915_private *i915)
 		struct super_block *sb = gemfs->mnt_sb;
 		/* FIXME: Disabled until we get W/A for read BW issue. */
 		char options[] = "huge=never";
-		int flags = 0;
-		int err;
-
-		err = sb->s_op->remount_fs(sb, &flags, options);
-		if (err) {
-			kern_unmount(gemfs);
-			return err;
-		}
+
+		ok = false;
+		fc = fs_context_for_reconfigure(sb->s_root, 0, 0);
+		if (IS_ERR(fc))
+			goto out;
+
+		if (!fc->ops->parse_monolithic ||
+				fc->ops->parse_monolithic(fc, options))
+			goto out;
+
+		if (fc->ops->reconfigure && !fc->ops->reconfigure(fc))
+			ok = true;
 	}
 
+out:
+	if (!ok)
+		dev_err(i915->drm.dev,
+			"Unable to reconfigure %s. %s\n",
+			"shmemfs for preferred allocation strategy",
+			"Continuing, but performance may suffer");
+	if (!IS_ERR_OR_NULL(fc))
+		put_fs_context(fc);
 	i915->mm.gemfs = gemfs;
-
 	return 0;
 }
 
-- 
2.22.0