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    Subject[PATCH 4.14 205/267] cgroup: pids: use atomic64_t for pids->limit
    Date
    From: Aleksa Sarai <cyphar@cyphar.com>

    commit a713af394cf382a30dd28a1015cbe572f1b9ca75 upstream.

    Because pids->limit can be changed concurrently (but we don't want to
    take a lock because it would be needlessly expensive), use atomic64_ts
    instead.

    Fixes: commit 49b786ea146f ("cgroup: implement the PIDs subsystem")
    Cc: stable@vger.kernel.org # v4.3+
    Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
    Signed-off-by: Tejun Heo <tj@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/cgroup/pids.c | 11 ++++++-----
    1 file changed, 6 insertions(+), 5 deletions(-)

    --- a/kernel/cgroup/pids.c
    +++ b/kernel/cgroup/pids.c
    @@ -48,7 +48,7 @@ struct pids_cgroup {
    * %PIDS_MAX = (%PID_MAX_LIMIT + 1).
    */
    atomic64_t counter;
    - int64_t limit;
    + atomic64_t limit;

    /* Handle for "pids.events" */
    struct cgroup_file events_file;
    @@ -76,8 +76,8 @@ pids_css_alloc(struct cgroup_subsys_stat
    if (!pids)
    return ERR_PTR(-ENOMEM);

    - pids->limit = PIDS_MAX;
    atomic64_set(&pids->counter, 0);
    + atomic64_set(&pids->limit, PIDS_MAX);
    atomic64_set(&pids->events_limit, 0);
    return &pids->css;
    }
    @@ -149,13 +149,14 @@ static int pids_try_charge(struct pids_c

    for (p = pids; parent_pids(p); p = parent_pids(p)) {
    int64_t new = atomic64_add_return(num, &p->counter);
    + int64_t limit = atomic64_read(&p->limit);

    /*
    * Since new is capped to the maximum number of pid_t, if
    * p->limit is %PIDS_MAX then we know that this test will never
    * fail.
    */
    - if (new > p->limit)
    + if (new > limit)
    goto revert;
    }

    @@ -280,7 +281,7 @@ set_limit:
    * Limit updates don't need to be mutex'd, since it isn't
    * critical that any racing fork()s follow the new limit.
    */
    - pids->limit = limit;
    + atomic64_set(&pids->limit, limit);
    return nbytes;
    }

    @@ -288,7 +289,7 @@ static int pids_max_show(struct seq_file
    {
    struct cgroup_subsys_state *css = seq_css(sf);
    struct pids_cgroup *pids = css_pids(css);
    - int64_t limit = pids->limit;
    + int64_t limit = atomic64_read(&pids->limit);

    if (limit >= PIDS_MAX)
    seq_printf(sf, "%s\n", PIDS_MAX_STR);

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