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

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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
This commit is contained in:
Linus Torvalds 2017-06-05 15:37:03 -07:00
commit ba7b2387ad
4 changed files with 28 additions and 2 deletions
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1
include/linux/cgroup-defs.h
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@ -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 */

20
include/linux/cgroup.h
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@ -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

5
kernel/cgroup/cgroup.c
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@ -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.

4
kernel/cgroup/cpuset.c
View File

@ -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)