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cgroups: fix probable race with put_css_set[_taskexit] and find_css_set

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put_css_set_taskexit may be called when find_css_set is called on other
cpu.  And the race will occur:

put_css_set_taskexit side                    find_css_set side

                                        |
atomic_dec_and_test(&kref->refcount)    |
    /* kref->refcount = 0 */            |
....................................................................
                                        |  read_lock(&css_set_lock)
                                        |  find_existing_css_set
                                        |  get_css_set
                                        |  read_unlock(&css_set_lock);
....................................................................
__release_css_set                       |
....................................................................
                                        | /* use a released css_set */
                                        |

[put_css_set is the same. But in the current code, all put_css_set are
put into cgroup mutex critical region as the same as find_css_set.]

[akpm@linux-foundation.org: repair comments]
[menage@google.com: eliminate race in css_set refcounting]
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Lai Jiangshan 2008-10-18 20:28:03 -07:00 • committed by Linus Torvalds
parent 248736c2a5
commit 146aa1bd05
3 changed files with 23 additions and 27 deletions
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4
kernel/cgroup_debug.c
View file

@ -57,7 +57,7 @@ static u64 current_css_set_refcount_read(struct cgroup *cont,
u64 count;
rcu_read_lock();
count = atomic_read(&current->cgroups->ref.refcount);
count = atomic_read(&current->cgroups->refcount);
rcu_read_unlock();
return count;
}
@ -90,7 +90,7 @@ static struct cftype files[] = {
{
.name = "releasable",
.read_u64 = releasable_read,
}
},
};
static int debug_populate(struct cgroup_subsys *ss, struct cgroup *cont)