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    Subject[patch 10/18] sched: allow for positional tg_tree walks
    Extend walk_tg_tree to accept a positional argument

    static int walk_tg_tree_from(struct task_group *from,
    tg_visitor down, tg_visitor up, void *data)

    Existing semantics are preserved, caller must hold rcu_lock() or sufficient
    analogue.

    Signed-off-by: Paul Turner <pjt@google.com>
    Reviewed-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>

    ---
    kernel/sched.c | 52 +++++++++++++++++++++++++++++++++++++++-------------
    1 file changed, 39 insertions(+), 13 deletions(-)

    Index: tip/kernel/sched.c
    ===================================================================
    --- tip.orig/kernel/sched.c
    +++ tip/kernel/sched.c
    @@ -1583,20 +1583,23 @@ static inline void dec_cpu_load(struct r
    typedef int (*tg_visitor)(struct task_group *, void *);

    /*
    - * Iterate the full tree, calling @down when first entering a node and @up when
    - * leaving it for the final time.
    + * Iterate task_group tree rooted at *from, calling @down when first entering a
    + * node and @up when leaving it for the final time.
    + *
    + * Caller must hold rcu_lock or sufficient equivalent.
    */
    -static int walk_tg_tree(tg_visitor down, tg_visitor up, void *data)
    +static int walk_tg_tree_from(struct task_group *from,
    + tg_visitor down, tg_visitor up, void *data)
    {
    struct task_group *parent, *child;
    int ret;

    - rcu_read_lock();
    - parent = &root_task_group;
    + parent = from;
    +
    down:
    ret = (*down)(parent, data);
    if (ret)
    - goto out_unlock;
    + goto out;
    list_for_each_entry_rcu(child, &parent->children, siblings) {
    parent = child;
    goto down;
    @@ -1605,19 +1608,29 @@ up:
    continue;
    }
    ret = (*up)(parent, data);
    - if (ret)
    - goto out_unlock;
    + if (ret || parent == from)
    + goto out;

    child = parent;
    parent = parent->parent;
    if (parent)
    goto up;
    -out_unlock:
    - rcu_read_unlock();
    -
    +out:
    return ret;
    }

    +/*
    + * Iterate the full tree, calling @down when first entering a node and @up when
    + * leaving it for the final time.
    + *
    + * Caller must hold rcu_lock or sufficient equivalent.
    + */
    +
    +static inline int walk_tg_tree(tg_visitor down, tg_visitor up, void *data)
    +{
    + return walk_tg_tree_from(&root_task_group, down, up, data);
    +}
    +
    static int tg_nop(struct task_group *tg, void *data)
    {
    return 0;
    @@ -1711,7 +1724,9 @@ static int tg_load_down(struct task_grou

    static void update_h_load(long cpu)
    {
    + rcu_read_lock();
    walk_tg_tree(tg_load_down, tg_nop, (void *)cpu);
    + rcu_read_unlock();
    }

    #endif
    @@ -8684,13 +8699,19 @@ static int tg_rt_schedulable(struct task

    static int __rt_schedulable(struct task_group *tg, u64 period, u64 runtime)
    {
    + int ret;
    +
    struct rt_schedulable_data data = {
    .tg = tg,
    .rt_period = period,
    .rt_runtime = runtime,
    };

    - return walk_tg_tree(tg_rt_schedulable, tg_nop, &data);
    + rcu_read_lock();
    + ret = walk_tg_tree(tg_rt_schedulable, tg_nop, &data);
    + rcu_read_unlock();
    +
    + return ret;
    }

    static int tg_set_rt_bandwidth(struct task_group *tg,
    @@ -9147,6 +9168,7 @@ static int tg_cfs_schedulable_down(struc

    static int __cfs_schedulable(struct task_group *tg, u64 period, u64 quota)
    {
    + int ret;
    struct cfs_schedulable_data data = {
    .tg = tg,
    .period = period,
    @@ -9158,7 +9180,11 @@ static int __cfs_schedulable(struct task
    do_div(data.quota, NSEC_PER_USEC);
    }

    - return walk_tg_tree(tg_cfs_schedulable_down, tg_nop, &data);
    + rcu_read_lock();
    + ret = walk_tg_tree(tg_cfs_schedulable_down, tg_nop, &data);
    + rcu_read_unlock();
    +
    + return ret;
    }
    #endif /* CONFIG_CFS_BANDWIDTH */
    #endif /* CONFIG_FAIR_GROUP_SCHED */



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