The static key __cfs_bandwidth_used is used to indicate whether bandwidth
control is enabled in the system. Currently, it is only decreased when a
task group disables bandwidth control. This is incorrect because if there
was a task group in the past that enabled bandwidth control, the
__cfs_bandwidth_used will never go to zero, even if there are no task_group
using bandwidth control now.
This patch tries to fix this issue by decrsasing bandwidth usage in
destroy_cfs_bandwidth(). cfs_bandwidth_usage_dec() calls
static_key_slow_dec_cpuslocked which needs to hold hotplug lock, but cfs
bandwidth destroy maybe run in a rcu callback. Move the call to
destroy_cfs_bandwidth() from unregister_fair_sched_group() to
cpu_cgroup_css_free() which runs in process context.
Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>
---
kernel/sched/core.c | 2 ++
kernel/sched/fair.c | 13 +++++++------
kernel/sched/sched.h | 2 ++
3 files changed, 11 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 6d35c48239be..7720d34bd71b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8816,6 +8816,8 @@ static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
{
struct task_group *tg = css_tg(css);
+ destroy_cfs_bandwidth(tg_cfs_bandwidth(tg));
+
/*
* Relies on the RCU grace period between css_released() and this.
*/
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index da3cdd86ab2e..c56b6d5b8ed7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5615,7 +5615,7 @@ void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b)
cfs_b->runtime_snap = cfs_b->runtime;
}
-static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
+struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
{
return &tg->cfs_bandwidth;
}
@@ -6438,7 +6438,7 @@ void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
hrtimer_start_expires(&cfs_b->period_timer, HRTIMER_MODE_ABS_PINNED);
}
-static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
+void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
{
int __maybe_unused i;
@@ -6472,6 +6472,9 @@ static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
local_irq_restore(flags);
}
#endif
+ guard(cpus_read_lock)();
+ if (cfs_b->quota != RUNTIME_INF)
+ cfs_bandwidth_usage_dec();
}
/*
@@ -6614,11 +6617,11 @@ void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b, struct cfs_bandwidth *paren
static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}
#endif
-static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
+struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
{
return NULL;
}
-static inline void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
+void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
static inline void update_runtime_enabled(struct rq *rq) {}
static inline void unthrottle_offline_cfs_rqs(struct rq *rq) {}
#ifdef CONFIG_CGROUP_SCHED
@@ -12992,8 +12995,6 @@ void unregister_fair_sched_group(struct task_group *tg)
struct rq *rq;
int cpu;
- destroy_cfs_bandwidth(tg_cfs_bandwidth(tg));
-
for_each_possible_cpu(cpu) {
if (tg->se[cpu])
remove_entity_load_avg(tg->se[cpu]);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 8a071022bdec..d251842867ce 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2938,6 +2938,8 @@ extern void init_dl_rq(struct dl_rq *dl_rq);
extern void cfs_bandwidth_usage_inc(void);
extern void cfs_bandwidth_usage_dec(void);
+extern struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg);
+extern void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b);
#ifdef CONFIG_NO_HZ_COMMON
#define NOHZ_BALANCE_KICK_BIT 0
--
2.20.1
On 2024/7/23 20:20, Chuyi Zhou wrote: > The static key __cfs_bandwidth_used is used to indicate whether bandwidth > control is enabled in the system. Currently, it is only decreased when a > task group disables bandwidth control. This is incorrect because if there > was a task group in the past that enabled bandwidth control, the > __cfs_bandwidth_used will never go to zero, even if there are no task_group > using bandwidth control now. > > This patch tries to fix this issue by decrsasing bandwidth usage in > destroy_cfs_bandwidth(). cfs_bandwidth_usage_dec() calls > static_key_slow_dec_cpuslocked which needs to hold hotplug lock, but cfs > bandwidth destroy maybe run in a rcu callback. Move the call to > destroy_cfs_bandwidth() from unregister_fair_sched_group() to > cpu_cgroup_css_free() which runs in process context. > > Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com> Yeah, autogroup can't have bandwidth set, so it's ok to just destroy bandwidth in .css_free(). Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev> Just some nits below: > --- > kernel/sched/core.c | 2 ++ > kernel/sched/fair.c | 13 +++++++------ > kernel/sched/sched.h | 2 ++ > 3 files changed, 11 insertions(+), 6 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 6d35c48239be..7720d34bd71b 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -8816,6 +8816,8 @@ static void cpu_cgroup_css_free(struct cgroup_subsys_state *css) > { > struct task_group *tg = css_tg(css); > > + destroy_cfs_bandwidth(tg_cfs_bandwidth(tg)); Instead of exporting this tg_cfs_bandwidth(), how about just changing the parameter of init_cfs_bandwidth()/destroy_cfs_bandwidth() to tg? Which maybe clearer? but this is your call. Thanks. > + > /* > * Relies on the RCU grace period between css_released() and this. > */ > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index da3cdd86ab2e..c56b6d5b8ed7 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5615,7 +5615,7 @@ void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b) > cfs_b->runtime_snap = cfs_b->runtime; > } > > -static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg) > +struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg) > { > return &tg->cfs_bandwidth; > } > @@ -6438,7 +6438,7 @@ void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b) > hrtimer_start_expires(&cfs_b->period_timer, HRTIMER_MODE_ABS_PINNED); > } > > -static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) > +void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) > { > int __maybe_unused i; > > @@ -6472,6 +6472,9 @@ static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) > local_irq_restore(flags); > } > #endif > + guard(cpus_read_lock)(); > + if (cfs_b->quota != RUNTIME_INF) > + cfs_bandwidth_usage_dec(); > } > > /* > @@ -6614,11 +6617,11 @@ void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b, struct cfs_bandwidth *paren > static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq) {} > #endif > > -static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg) > +struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg) > { > return NULL; > } > -static inline void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {} > +void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {} > static inline void update_runtime_enabled(struct rq *rq) {} > static inline void unthrottle_offline_cfs_rqs(struct rq *rq) {} > #ifdef CONFIG_CGROUP_SCHED > @@ -12992,8 +12995,6 @@ void unregister_fair_sched_group(struct task_group *tg) > struct rq *rq; > int cpu; > > - destroy_cfs_bandwidth(tg_cfs_bandwidth(tg)); > - > for_each_possible_cpu(cpu) { > if (tg->se[cpu]) > remove_entity_load_avg(tg->se[cpu]); > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 8a071022bdec..d251842867ce 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -2938,6 +2938,8 @@ extern void init_dl_rq(struct dl_rq *dl_rq); > extern void cfs_bandwidth_usage_inc(void); > extern void cfs_bandwidth_usage_dec(void); > > +extern struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg); > +extern void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b); > #ifdef CONFIG_NO_HZ_COMMON > > #define NOHZ_BALANCE_KICK_BIT 0
Chuyi Zhou <zhouchuyi@bytedance.com> writes: > The static key __cfs_bandwidth_used is used to indicate whether bandwidth > control is enabled in the system. Currently, it is only decreased when a > task group disables bandwidth control. This is incorrect because if there > was a task group in the past that enabled bandwidth control, the > __cfs_bandwidth_used will never go to zero, even if there are no task_group > using bandwidth control now. > > This patch tries to fix this issue by decrsasing bandwidth usage in > destroy_cfs_bandwidth(). cfs_bandwidth_usage_dec() calls > static_key_slow_dec_cpuslocked which needs to hold hotplug lock, but cfs > bandwidth destroy maybe run in a rcu callback. Move the call to > destroy_cfs_bandwidth() from unregister_fair_sched_group() to > cpu_cgroup_css_free() which runs in process context. > > Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com> Reviewed-By: Ben Segall <bsegall@google.com> > --- > kernel/sched/core.c | 2 ++ > kernel/sched/fair.c | 13 +++++++------ > kernel/sched/sched.h | 2 ++ > 3 files changed, 11 insertions(+), 6 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 6d35c48239be..7720d34bd71b 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -12992,8 +12995,6 @@ void unregister_fair_sched_group(struct task_group *tg) > struct rq *rq; > int cpu; > > - destroy_cfs_bandwidth(tg_cfs_bandwidth(tg)); > - > for_each_possible_cpu(cpu) { > if (tg->se[cpu]) > remove_entity_load_avg(tg->se[cpu]); There is a slightly subtle point here that autogroup cannot have a quota set. If there's some shenanigans way that that's possible then it would need a destroy as well. autogroup is already making assumptions anyways though.
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