diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index 21745946cae154f53cd87311e9350465388f70a5..ec47101cb1bf80f0867dbcff1d6aa10878df7418 100644 --- 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 --- 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 --- 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 --- 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)