Linux 5.0: Fix bio_set_dev()

The Linux 5.0 kernel updated the bio_set_dev() macro so it calls the
GPL-only bio_associate_blkg() symbol thus inadvertently converting
the entire macro.  Provide a minimal version which always assigns the
request queue's root_blkg to the bio.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes: openzfs#8287

config/kernel-bio_set_dev.m4

@@ -1,10 +1,10 @@
 dnl #
 dnl # Linux 4.14 API,
 dnl #
-dnl # The bio_set_dev() helper was introduced as part of the transition
+dnl # The bio_set_dev() helper macro was introduced as part of the transition
 dnl # to have struct gendisk in struct bio. 
 dnl #
-AC_DEFUN([ZFS_AC_KERNEL_BIO_SET_DEV], [
+AC_DEFUN([ZFS_AC_KERNEL_BIO_SET_DEV_MACRO], [
 	AC_MSG_CHECKING([whether bio_set_dev() exists])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/bio.h>
@@ -20,3 +20,34 @@ AC_DEFUN([ZFS_AC_KERNEL_BIO_SET_DEV], [
 		AC_MSG_RESULT(no)
 	])
 ])
+
+dnl #
+dnl # Linux 5.0 API,
+dnl #
+dnl # The bio_set_dev() helper macro was updated to internally depend on
+dnl # bio_associate_blkg() symbol which is exported GPL-only.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_BIO_SET_DEV_GPL_ONLY], [
+	AC_MSG_CHECKING([whether bio_set_dev() is GPL-only])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/module.h>
+		#include <linux/bio.h>
+		#include <linux/fs.h>
+		MODULE_LICENSE("$ZFS_META_LICENSE");
+	],[
+		struct block_device *bdev = NULL;
+		struct bio *bio = NULL;
+		bio_set_dev(bio, bdev);
+	],[
+		AC_MSG_RESULT(no)
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_BIO_SET_DEV_GPL_ONLY, 1,
+		    [bio_set_dev() GPL-only])
+	])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_BIO_SET_DEV], [
+	ZFS_AC_KERNEL_BIO_SET_DEV_MACRO
+	ZFS_AC_KERNEL_BIO_SET_DEV_GPL_ONLY
+])

module/zfs/vdev_disk.c

@@ -513,13 +513,38 @@ vdev_submit_bio_impl(struct bio *bio)
 #endif
 }
 
-#ifndef HAVE_BIO_SET_DEV
+#ifdef HAVE_BIO_SET_DEV
+#if defined(CONFIG_BLK_CGROUP) && defined(HAVE_BIO_SET_DEV_GPL_ONLY)
+/*
+ * The Linux 5.0 kernel updated the bio_set_dev() macro so it calls the
+ * GPL-only bio_associate_blkg() symbol thus inadvertently converting
+ * the entire macro.  Provide a minimal version which always assigns the
+ * request queue's root_blkg to the bio.
+ */
+static inline void
+vdev_bio_associate_blkg(struct bio *bio)
+{
+	struct request_queue *q = bio->bi_disk->queue;
+
+	ASSERT3P(q, !=, NULL);
+	ASSERT3P(q->root_blkg, !=, NULL);
+	ASSERT3P(bio->bi_blkg, ==, NULL);
+
+	if (blkg_tryget(q->root_blkg))
+		bio->bi_blkg = q->root_blkg;
+}
+#define	bio_associate_blkg vdev_bio_associate_blkg
+#endif
+#else
+/*
+ * Provide a bio_set_dev() helper macro for pre-Linux 4.14 kernels.
+ */
 static inline void
 bio_set_dev(struct bio *bio, struct block_device *bdev)
 {
 	bio->bi_bdev = bdev;
 }
-#endif /* !HAVE_BIO_SET_DEV */
+#endif /* HAVE_BIO_SET_DEV */
 
 static inline void
 vdev_submit_bio(struct bio *bio)