[tip: sched/core] sched: Inherit task cookie on fork()

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     85dd3f61203c5cfa72b308ff327b5fbf3fc1ce5e
Gitweb:        https://git.kernel.org/tip/85dd3f61203c5cfa72b308ff327b5fbf3fc1ce5e
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Mon, 29 Mar 2021 15:18:35 +02:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Wed, 12 May 2021 11:43:31 +02:00

sched: Inherit task cookie on fork()

Note that sched_core_fork() is called from under tasklist_lock, and
not from sched_fork() earlier. This avoids a few races later.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: Don Hiatt <dhiatt@xxxxxxxxxxxxxxxx>
Tested-by: Hongyu Ning <hongyu.ning@xxxxxxxxxxxxxxx>
Tested-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20210422123308.980003687@xxxxxxxxxxxxx
---
 include/linux/sched.h     | 2 ++
 kernel/fork.c             | 3 +++
 kernel/sched/core_sched.c | 6 ++++++
 3 files changed, 11 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index eab3f7c..fba47e5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2181,8 +2181,10 @@ const struct cpumask *sched_trace_rd_span(struct root_domain *rd);
 
 #ifdef CONFIG_SCHED_CORE
 extern void sched_core_free(struct task_struct *tsk);
+extern void sched_core_fork(struct task_struct *p);
 #else
 static inline void sched_core_free(struct task_struct *tsk) { }
+static inline void sched_core_fork(struct task_struct *p) { }
 #endif
 
 #endif
diff --git a/kernel/fork.c b/kernel/fork.c
index d16c60c..e7fd928 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2251,6 +2251,8 @@ static __latent_entropy struct task_struct *copy_process(
 
 	klp_copy_process(p);
 
+	sched_core_fork(p);
+
 	spin_lock(&current->sighand->siglock);
 
 	/*
@@ -2338,6 +2340,7 @@ static __latent_entropy struct task_struct *copy_process(
 	return p;
 
 bad_fork_cancel_cgroup:
+	sched_core_free(p);
 	spin_unlock(&current->sighand->siglock);
 	write_unlock_irq(&tasklist_lock);
 	cgroup_cancel_fork(p, args);
diff --git a/kernel/sched/core_sched.c b/kernel/sched/core_sched.c
index 8d0869a..dcbbeae 100644
--- a/kernel/sched/core_sched.c
+++ b/kernel/sched/core_sched.c
@@ -103,6 +103,12 @@ static unsigned long sched_core_clone_cookie(struct task_struct *p)
 	return cookie;
 }
 
+void sched_core_fork(struct task_struct *p)
+{
+	RB_CLEAR_NODE(&p->core_node);
+	p->core_cookie = sched_core_clone_cookie(current);
+}
+
 void sched_core_free(struct task_struct *p)
 {
 	sched_core_put_cookie(p->core_cookie);