mm: don't include <linux/blk-cgroup.h> in <linux/writeback.h>

blk-cgroup.h pulls in blkdev.h and thus pretty much all the block
headers.  Break this dependency chain by turning wbc_blkcg_css into a
macro and dropping the blk-cgroup.h include.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20210920123328.1399408-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/gpu/drm/i915/i915_utils.h

@@ -30,6 +30,7 @@
 #include <linux/sched.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
+#include <linux/sched/clock.h>
 
 struct drm_i915_private;
 struct timer_list;

fs/btrfs/inode.c

@@ -6,6 +6,7 @@
 #include <crypto/hash.h>
 #include <linux/kernel.h>
 #include <linux/bio.h>
+#include <linux/blk-cgroup.h>
 #include <linux/file.h>
 #include <linux/fs.h>
 #include <linux/pagemap.h>

fs/quota/quota.c

@@ -10,6 +10,7 @@
 #include <linux/namei.h>
 #include <linux/slab.h>
 #include <asm/current.h>
+#include <linux/blkdev.h>
 #include <linux/uaccess.h>
 #include <linux/kernel.h>
 #include <linux/security.h>

include/linux/writeback.h

@@ -11,7 +11,6 @@
 #include <linux/flex_proportions.h>
 #include <linux/backing-dev-defs.h>
 #include <linux/blk_types.h>
-#include <linux/blk-cgroup.h>
 
 struct bio;
 
@@ -109,15 +108,12 @@ static inline int wbc_to_write_flags(struct writeback_control *wbc)
 	return flags;
 }
 
-static inline struct cgroup_subsys_state *
-wbc_blkcg_css(struct writeback_control *wbc)
-{
 #ifdef CONFIG_CGROUP_WRITEBACK
-	if (wbc->wb)
-		return wbc->wb->blkcg_css;
-#endif
-	return blkcg_root_css;
-}
+#define wbc_blkcg_css(wbc) \
+	((wbc)->wb ? (wbc)->wb->blkcg_css : blkcg_root_css)
+#else
+#define wbc_blkcg_css(wbc)		(blkcg_root_css)
+#endif /* CONFIG_CGROUP_WRITEBACK */
 
 /*
  * A wb_domain represents a domain that wb's (bdi_writeback's) belong to

lib/random32.c

@@ -39,6 +39,7 @@
 #include <linux/random.h>
 #include <linux/sched.h>
 #include <linux/bitops.h>
+#include <linux/slab.h>
 #include <asm/unaligned.h>
 #include <trace/events/random.h>