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Date: Mon, 14 Feb 2022 10:16:57 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Borislav Petkov <bp@...e.de>,
Tadeusz Struk <tadeusz.struk@...aro.org>,
x86-ml <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
zhangqiao22@...wei.com, tj@...nel.org, dietmar.eggemann@....com
Subject: Re: [GIT PULL] sched/urgent for 5.17-rc4
On Mon, Feb 14, 2022 at 09:45:22AM +0100, Peter Zijlstra wrote:
> On Sun, Feb 13, 2022 at 10:02:22AM -0800, Linus Torvalds wrote:
> > On Sun, Feb 13, 2022 at 4:37 AM Borislav Petkov <bp@...e.de> wrote:
> > >
> > > Tadeusz Struk (1):
> > > sched/fair: Fix fault in reweight_entity
> >
> > I've pulled this, but this really smells bad to me.
> >
> > If set_load_weight() can see a process that hasn't even had the
> > runqueue pointer set yet, then what keeps *others* from the same
> > thing?
>
> Urgh, I think you're right, the moment we enter the pidhash and become
> visible we should be complete. That means the previous commit
> (4ef0c5c6b5ba) is buggered... Let me try and make sense of all that
> cgroup stuff again :-(
Zhang, Tadeusz, TJ, how does this look?
---
include/linux/sched/task.h | 4 ++--
kernel/fork.c | 9 ++++++++-
kernel/sched/core.c | 34 +++++++++++++++++++++-------------
3 files changed, 31 insertions(+), 16 deletions(-)
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index b9198a1b3a84..e84e54d1b490 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -54,8 +54,8 @@ extern asmlinkage void schedule_tail(struct task_struct *prev);
extern void init_idle(struct task_struct *idle, int cpu);
extern int sched_fork(unsigned long clone_flags, struct task_struct *p);
-extern void sched_post_fork(struct task_struct *p,
- struct kernel_clone_args *kargs);
+extern void sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs);
+extern void sched_post_fork(struct task_struct *p);
extern void sched_dead(struct task_struct *p);
void __noreturn do_task_dead(void);
diff --git a/kernel/fork.c b/kernel/fork.c
index d75a528f7b21..05faebafe2b5 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2266,6 +2266,13 @@ static __latent_entropy struct task_struct *copy_process(
if (retval)
goto bad_fork_put_pidfd;
+ /*
+ * Now that the cgroups are pinned, re-clone the parent cgroup and put
+ * the new task on the correct runqueue. All this *before* the task
+ * becomes visible.
+ */
+ sched_cgroup_fork(p, args);
+
/*
* From this point on we must avoid any synchronous user-space
* communication until we take the tasklist-lock. In particular, we do
@@ -2376,7 +2383,7 @@ static __latent_entropy struct task_struct *copy_process(
write_unlock_irq(&tasklist_lock);
proc_fork_connector(p);
- sched_post_fork(p, args);
+ sched_post_fork(p);
cgroup_post_fork(p, args);
perf_event_fork(p);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fcf0c180617c..dd97a42b1eee 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1214,9 +1214,8 @@ int tg_nop(struct task_group *tg, void *data)
}
#endif
-static void set_load_weight(struct task_struct *p)
+static void set_load_weight(struct task_struct *p, bool update_load)
{
- bool update_load = !(READ_ONCE(p->__state) & TASK_NEW);
int prio = p->static_prio - MAX_RT_PRIO;
struct load_weight *load = &p->se.load;
@@ -4407,7 +4406,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
p->static_prio = NICE_TO_PRIO(0);
p->prio = p->normal_prio = p->static_prio;
- set_load_weight(p);
+ set_load_weight(p, false);
/*
* We don't need the reset flag anymore after the fork. It has
@@ -4425,6 +4424,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
init_entity_runnable_average(&p->se);
+
#ifdef CONFIG_SCHED_INFO
if (likely(sched_info_on()))
memset(&p->sched_info, 0, sizeof(p->sched_info));
@@ -4440,18 +4440,23 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
return 0;
}
-void sched_post_fork(struct task_struct *p, struct kernel_clone_args *kargs)
+void sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs)
{
unsigned long flags;
-#ifdef CONFIG_CGROUP_SCHED
- struct task_group *tg;
-#endif
+ /*
+ * Because we're not yet on the pid-hash, p->pi_lock isn't strictly
+ * required yet, but lockdep gets upset if rules are violated.
+ */
raw_spin_lock_irqsave(&p->pi_lock, flags);
#ifdef CONFIG_CGROUP_SCHED
- tg = container_of(kargs->cset->subsys[cpu_cgrp_id],
- struct task_group, css);
- p->sched_task_group = autogroup_task_group(p, tg);
+ if (1) {
+ struct task_group *tg;
+ tg = container_of(kargs->cset->subsys[cpu_cgrp_id],
+ struct task_group, css);
+ tg = autogroup_task_group(p, tg);
+ p->sched_task_group = autogroup_task_group(p, tg);
+ }
#endif
rseq_migrate(p);
/*
@@ -4462,7 +4467,10 @@ void sched_post_fork(struct task_struct *p, struct kernel_clone_args *kargs)
if (p->sched_class->task_fork)
p->sched_class->task_fork(p);
raw_spin_unlock_irqrestore(&p->pi_lock, flags);
+}
+void sched_post_fork(struct task_struct *p)
+{
uclamp_post_fork(p);
}
@@ -6922,7 +6930,7 @@ void set_user_nice(struct task_struct *p, long nice)
put_prev_task(rq, p);
p->static_prio = NICE_TO_PRIO(nice);
- set_load_weight(p);
+ set_load_weight(p, true);
old_prio = p->prio;
p->prio = effective_prio(p);
@@ -7213,7 +7221,7 @@ static void __setscheduler_params(struct task_struct *p,
*/
p->rt_priority = attr->sched_priority;
p->normal_prio = normal_prio(p);
- set_load_weight(p);
+ set_load_weight(p, true);
}
/*
@@ -9446,7 +9454,7 @@ void __init sched_init(void)
#endif
}
- set_load_weight(&init_task);
+ set_load_weight(&init_task, false);
/*
* The boot idle thread does lazy MMU switching as well:
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