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Message-ID: <164526567729.16921.5416435160262961553.tip-bot2@tip-bot2>
Date: Sat, 19 Feb 2022 10:14:37 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Tadeusz Struk <tadeusz.struk@...aro.org>,
Zhang Qiao <zhangqiao22@...wei.com>,
Dietmar Eggemann <dietmar.eggemann@....com>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: sched/urgent] sched: Fix yet more sched_fork() races
The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: b1e8206582f9d680cff7d04828708c8b6ab32957
Gitweb: https://git.kernel.org/tip/b1e8206582f9d680cff7d04828708c8b6ab32957
Author: Peter Zijlstra <peterz@...radead.org>
AuthorDate: Mon, 14 Feb 2022 10:16:57 +01:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Sat, 19 Feb 2022 11:11:05 +01:00
sched: Fix yet more sched_fork() races
Where commit 4ef0c5c6b5ba ("kernel/sched: Fix sched_fork() access an
invalid sched_task_group") fixed a fork race vs cgroup, it opened up a
race vs syscalls by not placing the task on the runqueue before it
gets exposed through the pidhash.
Commit 13765de8148f ("sched/fair: Fix fault in reweight_entity") is
trying to fix a single instance of this, instead fix the whole class
of issues, effectively reverting this commit.
Fixes: 4ef0c5c6b5ba ("kernel/sched: Fix sched_fork() access an invalid sched_task_group")
Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Tadeusz Struk <tadeusz.struk@...aro.org>
Tested-by: Zhang Qiao <zhangqiao22@...wei.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@....com>
Link: https://lkml.kernel.org/r/YgoeCbwj5mbCR0qA@hirez.programming.kicks-ass.net
---
include/linux/sched/task.h | 4 ++--
kernel/fork.c | 13 ++++++++++++-
kernel/sched/core.c | 34 +++++++++++++++++++++-------------
3 files changed, 35 insertions(+), 16 deletions(-)
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index b9198a1..e84e54d 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 d75a528..c607d23 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2267,6 +2267,17 @@ static __latent_entropy struct task_struct *copy_process(
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.
+ *
+ * This isn't part of ->can_fork() because while the re-cloning is
+ * cgroup specific, it unconditionally needs to place the task on a
+ * runqueue.
+ */
+ 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
* not want user-space to be able to predict the process start-time by
@@ -2376,7 +2387,7 @@ 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 fcf0c18..9745613 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 = 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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