From: Qais Yousef qais.yousef@arm.com
[ Upstream commit 0213b7083e81f4acd69db32cb72eb4e5f220329a ]
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_...
Fixes: 0c18f2ecfcc2 ("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 Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/core.c | 49 +++++++++++++++++---------------------------- 1 file changed, 18 insertions(+), 31 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d4bbead59ad2..679562d2f55d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1063,8 +1063,10 @@ static void uclamp_sync_util_min_rt_default(void) static inline struct uclamp_se uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id) { + /* Copy by value as we could modify it */ struct uclamp_se uc_req = p->uclamp_req[clamp_id]; #ifdef CONFIG_UCLAMP_TASK_GROUP + unsigned int tg_min, tg_max, value;
/* * Tasks in autogroups or root task group will be @@ -1075,23 +1077,11 @@ uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id) if (task_group(p) == &root_task_group) return uc_req;
- switch (clamp_id) { - case UCLAMP_MIN: { - struct uclamp_se uc_min = task_group(p)->uclamp[clamp_id]; - if (uc_req.value < uc_min.value) - return uc_min; - break; - } - case UCLAMP_MAX: { - struct uclamp_se uc_max = task_group(p)->uclamp[clamp_id]; - if (uc_req.value > uc_max.value) - return uc_max; - break; - } - default: - WARN_ON_ONCE(1); - break; - } + tg_min = task_group(p)->uclamp[UCLAMP_MIN].value; + tg_max = task_group(p)->uclamp[UCLAMP_MAX].value; + value = uc_req.value; + value = clamp(value, tg_min, tg_max); + uclamp_se_set(&uc_req, value, false); #endif
return uc_req; @@ -1290,8 +1280,9 @@ static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) }
static inline void -uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id) +uclamp_update_active(struct task_struct *p) { + enum uclamp_id clamp_id; struct rq_flags rf; struct rq *rq;
@@ -1311,9 +1302,11 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id) * affecting a valid clamp bucket, the next time it's enqueued, * it will already see the updated clamp bucket value. */ - if (p->uclamp[clamp_id].active) { - uclamp_rq_dec_id(rq, p, clamp_id); - uclamp_rq_inc_id(rq, p, clamp_id); + for_each_clamp_id(clamp_id) { + if (p->uclamp[clamp_id].active) { + uclamp_rq_dec_id(rq, p, clamp_id); + uclamp_rq_inc_id(rq, p, clamp_id); + } }
task_rq_unlock(rq, p, &rf); @@ -1321,20 +1314,14 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
#ifdef CONFIG_UCLAMP_TASK_GROUP static inline void -uclamp_update_active_tasks(struct cgroup_subsys_state *css, - unsigned int clamps) +uclamp_update_active_tasks(struct cgroup_subsys_state *css) { - enum uclamp_id clamp_id; struct css_task_iter it; struct task_struct *p;
css_task_iter_start(css, 0, &it); - while ((p = css_task_iter_next(&it))) { - for_each_clamp_id(clamp_id) { - if ((0x1 << clamp_id) & clamps) - uclamp_update_active(p, clamp_id); - } - } + while ((p = css_task_iter_next(&it))) + uclamp_update_active(p); css_task_iter_end(&it); }
@@ -7749,7 +7736,7 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css) }
/* Immediately update descendants RUNNABLE tasks */ - uclamp_update_active_tasks(css, clamps); + uclamp_update_active_tasks(css); } }