blkcg: revert blkcg cleanups series

This reverts a series committed earlier due to null pointer exception
bug report in [1]. It seems there are edge case interactions that I did
not consider and will need some time to understand what causes the
adverse interactions.

The original series can be found in [2] with a follow up series in [3].

[1] https://www.spinics.net/lists/cgroups/msg20719.html
[2] https://lore.kernel.org/lkml/20180911184137.35897-1-dennisszhou@gmail.com/
[3] https://lore.kernel.org/lkml/20181020185612.51587-1-dennis@kernel.org/

This reverts the following commits:
d459d853c2ed, b2c3fa546705, 101246ec02b5, b3b9f24f5fcc, e2b0989954ae,
f0fcb3ec89f3, c839e7a03f92, bdc2491708c4, 74b7c02a9bc1, 5bf9a1f3b4ef,
a7b39b4e961c, 07b05bcc3213, 49f4c2dc2b50, 27e6fa996c53

Signed-off-by: Dennis Zhou <dennis@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

2 files changed, 11 insertions, 41 deletions

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 4c1cf0969a80..4a3dae2a8283 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -492,7 +492,7 @@ static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
 }
 
 /**
- * cgroup_e_css_by_mask - obtain a cgroup's effective css for the specified ss
+ * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
  * @cgrp: the cgroup of interest
  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
  *
@@ -501,8 +501,8 @@ static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
  * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
  * function is guaranteed to return non-NULL css.
  */
-static struct cgroup_subsys_state *cgroup_e_css_by_mask(struct cgroup *cgrp,
-							struct cgroup_subsys *ss)
+static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
+						struct cgroup_subsys *ss)
 {
 	lockdep_assert_held(&cgroup_mutex);
 
@@ -523,35 +523,6 @@ static struct cgroup_subsys_state *cgroup_e_css_by_mask(struct cgroup *cgrp,
 }
 
 /**
- * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
- * @cgrp: the cgroup of interest
- * @ss: the subsystem of interest
- *
- * Find and get the effective css of @cgrp for @ss.  The effective css is
- * defined as the matching css of the nearest ancestor including self which
- * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
- * the root css is returned, so this function always returns a valid css.
- *
- * The returned css is not guaranteed to be online, and therefore it is the
- * callers responsiblity to tryget a reference for it.
- */
-struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
-					 struct cgroup_subsys *ss)
-{
-	struct cgroup_subsys_state *css;
-
-	do {
-		css = cgroup_css(cgrp, ss);
-
-		if (css)
-			return css;
-		cgrp = cgroup_parent(cgrp);
-	} while (cgrp);
-
-	return init_css_set.subsys[ss->id];
-}
-
-/**
  * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
  * @cgrp: the cgroup of interest
  * @ss: the subsystem of interest
@@ -633,11 +604,10 @@ EXPORT_SYMBOL_GPL(of_css);
  *
  * Should be called under cgroup_[tree_]mutex.
  */
-#define for_each_e_css(css, ssid, cgrp)					    \
-	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	    \
-		if (!((css) = cgroup_e_css_by_mask(cgrp,		    \
-						   cgroup_subsys[(ssid)]))) \
-			;						    \
+#define for_each_e_css(css, ssid, cgrp)					\
+	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	\
+		if (!((css) = cgroup_e_css(cgrp, cgroup_subsys[(ssid)]))) \
+			;						\
 		else
 
 /**
@@ -1036,7 +1006,7 @@ static struct css_set *find_existing_css_set(struct css_set *old_cset,
 			 * @ss is in this hierarchy, so we want the
 			 * effective css from @cgrp.
 			 */
-			template[i] = cgroup_e_css_by_mask(cgrp, ss);
+			template[i] = cgroup_e_css(cgrp, ss);
 		} else {
 			/*
 			 * @ss is not in this hierarchy, so we don't want
@@ -3053,7 +3023,7 @@ static int cgroup_apply_control(struct cgroup *cgrp)
 		return ret;
 
 	/*
-	 * At this point, cgroup_e_css_by_mask() results reflect the new csses
+	 * At this point, cgroup_e_css() results reflect the new csses
 	 * making the following cgroup_update_dfl_csses() properly update
 	 * css associations of all tasks in the subtree.
 	 */
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index fac0ddf8a8e2..2868d85f1fb1 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -764,9 +764,9 @@ blk_trace_bio_get_cgid(struct request_queue *q, struct bio *bio)
 	if (!bt || !(blk_tracer_flags.val & TRACE_BLK_OPT_CGROUP))
 		return NULL;
 
-	if (!bio->bi_blkg)
+	if (!bio->bi_css)
 		return NULL;
-	return cgroup_get_kernfs_id(bio_blkcg(bio)->css.cgroup);
+	return cgroup_get_kernfs_id(bio->bi_css->cgroup);
 }
 #else
 static union kernfs_node_id *