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

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.]

[[email protected]: repair comments]
[[email protected]: eliminate race in css_set refcounting]
Signed-off-by: Lai Jiangshan <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Signed-off-by: Paul Menage <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions