sched/uclamp: Fix uclamp_tg_restrict()
Now cpu.uclamp.min acts as a protection, we need to make sure that the
uclamp request of the task is within the allowed range of the cgroup,
that is it is clamp()'ed correctly by tg->uclamp[UCLAMP_MIN] and
tg->uclamp[UCLAMP_MAX].
As reported by Xuewen [1] we can have some corner cases where there's
inversion between uclamp requested by task (p) and the uclamp values of
the taskgroup it's attached to (tg). Following table demonstrates
2 corner cases:
| p | tg | effective
-----------+-----+------+-----------
CASE 1
-----------+-----+------+-----------
uclamp_min | 60% | 0% | 60%
-----------+-----+------+-----------
uclamp_max | 80% | 50% | 50%
-----------+-----+------+-----------
CASE 2
-----------+-----+------+-----------
uclamp_min | 0% | 30% | 30%
-----------+-----+------+-----------
uclamp_max | 20% | 50% | 20%
-----------+-----+------+-----------
With this fix we get:
| p | tg | effective
-----------+-----+------+-----------
CASE 1
-----------+-----+------+-----------
uclamp_min | 60% | 0% | 50%
-----------+-----+------+-----------
uclamp_max | 80% | 50% | 50%
-----------+-----+------+-----------
CASE 2
-----------+-----+------+-----------
uclamp_min | 0% | 30% | 30%
-----------+-----+------+-----------
uclamp_max | 20% | 50% | 30%
-----------+-----+------+-----------
Additionally uclamp_update_active_tasks() must now unconditionally
update both UCLAMP_MIN/MAX because changing the tg's UCLAMP_MAX for
instance could have an impact on the effective UCLAMP_MIN of the tasks.
| p | tg | effective
-----------+-----+------+-----------
old
-----------+-----+------+-----------
uclamp_min | 60% | 0% | 50%
-----------+-----+------+-----------
uclamp_max | 80% | 50% | 50%
-----------+-----+------+-----------
*new*
-----------+-----+------+-----------
uclamp_min | 60% | 0% | *60%*
-----------+-----+------+-----------
uclamp_max | 80% |*70%* | *70%*
-----------+-----+------+-----------
[1] https://lore.kernel.org/lkml/CAB8ipk_a6VFNjiEnHRHkUMBKbA+qzPQvhtNjJ_YNzQhqV_o8Zw@mail.gmail.com/
Fixes: 0c18f2ecfc
("sched/uclamp: Fix wrong implementation of cpu.uclamp.min")
Reported-by: Xuewen Yan <xuewen.yan94@gmail.com>
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210617165155.3774110-1-qais.yousef@arm.com
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@ -1403,8 +1403,10 @@ static void uclamp_sync_util_min_rt_default(void)
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static inline struct uclamp_se
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uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
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{
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/* Copy by value as we could modify it */
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struct uclamp_se uc_req = p->uclamp_req[clamp_id];
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#ifdef CONFIG_UCLAMP_TASK_GROUP
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unsigned int tg_min, tg_max, value;
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/*
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* Tasks in autogroups or root task group will be
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@ -1415,23 +1417,11 @@ uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
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if (task_group(p) == &root_task_group)
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return uc_req;
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switch (clamp_id) {
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case UCLAMP_MIN: {
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struct uclamp_se uc_min = task_group(p)->uclamp[clamp_id];
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if (uc_req.value < uc_min.value)
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return uc_min;
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break;
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}
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case UCLAMP_MAX: {
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struct uclamp_se uc_max = task_group(p)->uclamp[clamp_id];
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if (uc_req.value > uc_max.value)
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return uc_max;
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break;
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}
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default:
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WARN_ON_ONCE(1);
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break;
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}
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tg_min = task_group(p)->uclamp[UCLAMP_MIN].value;
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tg_max = task_group(p)->uclamp[UCLAMP_MAX].value;
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value = uc_req.value;
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value = clamp(value, tg_min, tg_max);
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uclamp_se_set(&uc_req, value, false);
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#endif
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return uc_req;
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@ -1630,8 +1620,9 @@ static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
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}
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static inline void
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uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
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uclamp_update_active(struct task_struct *p)
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{
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enum uclamp_id clamp_id;
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struct rq_flags rf;
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struct rq *rq;
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@ -1651,9 +1642,11 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
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* affecting a valid clamp bucket, the next time it's enqueued,
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* it will already see the updated clamp bucket value.
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*/
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if (p->uclamp[clamp_id].active) {
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uclamp_rq_dec_id(rq, p, clamp_id);
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uclamp_rq_inc_id(rq, p, clamp_id);
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for_each_clamp_id(clamp_id) {
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if (p->uclamp[clamp_id].active) {
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uclamp_rq_dec_id(rq, p, clamp_id);
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uclamp_rq_inc_id(rq, p, clamp_id);
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}
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}
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task_rq_unlock(rq, p, &rf);
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@ -1661,20 +1654,14 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
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#ifdef CONFIG_UCLAMP_TASK_GROUP
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static inline void
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uclamp_update_active_tasks(struct cgroup_subsys_state *css,
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unsigned int clamps)
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uclamp_update_active_tasks(struct cgroup_subsys_state *css)
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{
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enum uclamp_id clamp_id;
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struct css_task_iter it;
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struct task_struct *p;
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css_task_iter_start(css, 0, &it);
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while ((p = css_task_iter_next(&it))) {
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for_each_clamp_id(clamp_id) {
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if ((0x1 << clamp_id) & clamps)
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uclamp_update_active(p, clamp_id);
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}
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}
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while ((p = css_task_iter_next(&it)))
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uclamp_update_active(p);
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css_task_iter_end(&it);
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}
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@ -9634,7 +9621,7 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css)
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}
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/* Immediately update descendants RUNNABLE tasks */
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uclamp_update_active_tasks(css, clamps);
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uclamp_update_active_tasks(css);
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}
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}
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