[PATCH 4/9] sched: Default core-sched policy

[Peter Zijlstra <peterz@infradead.org>]

Implement default core scheduling policy.

 - fork() / clone(): inherit cookie from parent
 - exec(): if cookie then new cookie

Did that exec() thing want to change cookie on suid instead, just like
perf_event_exit_task() ?

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@infradead.org>
---
 fs/exec.c                  |    4 +++-
 include/linux/sched.h      |    4 ++++
 include/linux/sched/task.h |    4 ++--
 kernel/fork.c              |    3 +++
 kernel/sched/core.c        |   11 +++++++++--
 kernel/sched/core_sched.c  |   21 +++++++++++++++++++++
 6 files changed, 42 insertions(+), 5 deletions(-)

--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1807,7 +1807,9 @@ static int bprm_execve(struct linux_binp
 	if (IS_ERR(file))
 		goto out_unmark;
 
-	sched_exec();
+	retval = sched_exec();
+	if (retval)
+		goto out;
 
 	bprm->file = file;
 	/*
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2171,8 +2171,12 @@ const struct cpumask *sched_trace_rd_spa
 
 #ifdef CONFIG_SCHED_CORE
 extern void sched_core_free(struct task_struct *tsk);
+extern int sched_core_exec(void);
+extern void sched_core_fork(struct task_struct *p);
 #else
 static inline void sched_core_free(struct task_struct *tsk) { }
+static inline int sched_core_exec(void) { return 0; }
+static inline void sched_core_fork(struct task_struct *p) { }
 #endif
 
 #endif
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -94,9 +94,9 @@ extern void free_task(struct task_struct
 
 /* sched_exec is called by processes performing an exec */
 #ifdef CONFIG_SMP
-extern void sched_exec(void);
+extern int sched_exec(void);
 #else
-#define sched_exec()   {}
+static inline int sched_exec(void) { return 0; }
 #endif
 
 static inline struct task_struct *get_task_struct(struct task_struct *t)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2242,6 +2242,8 @@ static __latent_entropy struct task_stru
 
 	klp_copy_process(p);
 
+	sched_core_fork(p);
+
 	spin_lock(&current->sighand->siglock);
 
 	/*
@@ -2329,6 +2331,7 @@ static __latent_entropy struct task_stru
 	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);
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4762,11 +4762,17 @@ unsigned long nr_iowait(void)
  * sched_exec - execve() is a valuable balancing opportunity, because at
  * this point the task has the smallest effective memory and cache footprint.
  */
-void sched_exec(void)
+int sched_exec(void)
 {
 	struct task_struct *p = current;
 	unsigned long flags;
 	int dest_cpu;
+	int ret;
+
+	/* this may change what tasks current can share a core with */
+	ret = sched_core_exec();
+	if (ret)
+		return ret;
 
 	raw_spin_lock_irqsave(&p->pi_lock, flags);
 	dest_cpu = p->sched_class->select_task_rq(p, task_cpu(p), WF_EXEC);
@@ -4778,10 +4784,11 @@ void sched_exec(void)
 
 		raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 		stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
-		return;
+		return 0;
 	}
 unlock:
 	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
+	return 0;
 }
 
 #endif
--- a/kernel/sched/core_sched.c
+++ b/kernel/sched/core_sched.c
@@ -100,7 +100,28 @@ static unsigned long sched_core_clone_co
 	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);
 }
+
+int sched_core_exec(void)
+{
+	/* absent a policy mech, if task had a cookie, give it a new one */
+	if (current->core_cookie) {
+		unsigned long cookie = sched_core_alloc_cookie();
+		if (!cookie)
+			return -ENOMEM;
+		cookie = sched_core_update_cookie(current, cookie);
+		sched_core_put_cookie(cookie);
+	}
+
+	return 0;
+}
+