Merge branch 'for-4.12-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj...

Pull cgroup fixes from Tejun Heo:
 "Two cgroup fixes. One to address RCU delay of cpuset removal affecting
  userland visible behaviors. The other fixes a race condition between
  controller disable and cgroup removal"

* 'for-4.12-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cpuset: consider dying css as offline
  cgroup: Prevent kill_css() from being called more than once

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 21745946cae154f53cd87311e9350465388f70a5..ec47101cb1bf80f0867dbcff1d6aa10878df7418 100644 (file)
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -48,6 +48,7 @@ enum {
        CSS_ONLINE      = (1 << 1), /* between ->css_online() and ->css_offline() */
        CSS_RELEASED    = (1 << 2), /* refcnt reached zero, released */
        CSS_VISIBLE     = (1 << 3), /* css is visible to userland */
+       CSS_DYING       = (1 << 4), /* css is dying */
 };
 
 /* bits in struct cgroup flags field */

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index ed2573e149faf070714e04f8160f7056b2fb1d3e..710a005c6b7a652bb9c32b5457dbd64196f6f4a0 100644 (file)
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -343,6 +343,26 @@ static inline bool css_tryget_online(struct cgroup_subsys_state *css)
        return true;
 }
 
+/**
+ * css_is_dying - test whether the specified css is dying
+ * @css: target css
+ *
+ * Test whether @css is in the process of offlining or already offline.  In
+ * most cases, ->css_online() and ->css_offline() callbacks should be
+ * enough; however, the actual offline operations are RCU delayed and this
+ * test returns %true also when @css is scheduled to be offlined.
+ *
+ * This is useful, for example, when the use case requires synchronous
+ * behavior with respect to cgroup removal.  cgroup removal schedules css
+ * offlining but the css can seem alive while the operation is being
+ * delayed.  If the delay affects user visible semantics, this test can be
+ * used to resolve the situation.
+ */
+static inline bool css_is_dying(struct cgroup_subsys_state *css)
+{
+       return !(css->flags & CSS_NO_REF) && percpu_ref_is_dying(&css->refcnt);
+}
+
 /**
  * css_put - put a css reference
  * @css: target css

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index c3c9a0e1b3c9a474bd80b8cb10ea1049284474b0..8d4e85eae42c08481899e415075ee42c6d12f90f 100644 (file)
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4265,6 +4265,11 @@ static void kill_css(struct cgroup_subsys_state *css)
 {
        lockdep_assert_held(&cgroup_mutex);
 
+       if (css->flags & CSS_DYING)
+               return;
+
+       css->flags |= CSS_DYING;
+
        /*
         * This must happen before css is disassociated with its cgroup.
         * See seq_css() for details.

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index f6501f4f6040b5a9c21e84aeb57e20906ef1c614..ae643412948added94f05d7efb120631f7798b44 100644 (file)
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -176,9 +176,9 @@ typedef enum {
 } cpuset_flagbits_t;
 
 /* convenient tests for these bits */
-static inline bool is_cpuset_online(const struct cpuset *cs)
+static inline bool is_cpuset_online(struct cpuset *cs)
 {
-       return test_bit(CS_ONLINE, &cs->flags);
+       return test_bit(CS_ONLINE, &cs->flags) && !css_is_dying(&cs->css);
 }
 
 static inline int is_cpu_exclusive(const struct cpuset *cs)