[PATCH v7 11/22] sched: Introduce task_struct::user_cpus_ptr to track requested affinity

Will Deacon
2021-05-25T15:23:26Z

In preparation for saving and restoring the user-requested CPU affinity
mask of a task, add a new cpumask_t pointer to 'struct task_struct'.

If the pointer is non-NULL, then the mask is copied across fork() and
freed on task exit.

Signed-off-by: Will Deacon <will@kernel.org>
---
include/linux/sched.h | 13 +++++++++++++
init/init_task.c | 1 +
kernel/fork.c | 2 ++
kernel/sched/core.c | 20 ++++++++++++++++++++
4 files changed, 36 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d2c881384517..db32d4f7e5b3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -730,6 +730,7 @@ struct task_struct {
unsigned int policy;
int nr_cpus_allowed;
const cpumask_t *cpus_ptr;
+ cpumask_t *user_cpus_ptr;
cpumask_t cpus_mask;
void *migration_pending;
#ifdef CONFIG_SMP
@@ -1688,6 +1689,8 @@ extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_
#ifdef CONFIG_SMP
extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask);
extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);
+extern int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, int node);
+extern void release_user_cpus_ptr(struct task_struct *p);
#else
static inline void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
{
@@ -1698,6 +1701,16 @@ static inline int set_cpus_allowed_ptr(struct task_struct *p, const struct cpuma
return -EINVAL;
return 0;
}
+static inline int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, int node)
+{
+ if (src->user_cpus_ptr)
+ return -EINVAL;
+ return 0;
+}
+static inline void release_user_cpus_ptr(struct task_struct *p)
+{
+ WARN_ON(p->user_cpus_ptr);
+}
#endif

extern int yield_to(struct task_struct *p, bool preempt);
diff --git a/init/init_task.c b/init/init_task.c
index 8b08c2e19cbb..158c2b1689e1 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -80,6 +80,7 @@ struct task_struct init_task
.normal_prio = MAX_PRIO - 20,
.policy = SCHED_NORMAL,
.cpus_ptr = &init_task.cpus_mask,
+ .user_cpus_ptr = NULL,
.cpus_mask = CPU_MASK_ALL,
.nr_cpus_allowed= NR_CPUS,
.mm = NULL,
diff --git a/kernel/fork.c b/kernel/fork.c
index dc06afd725cb..d3710e7f1686 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -446,6 +446,7 @@ void put_task_stack(struct task_struct *tsk)

void free_task(struct task_struct *tsk)
{
+ release_user_cpus_ptr(tsk);
scs_release(tsk);

#ifndef CONFIG_THREAD_INFO_IN_TASK
@@ -918,6 +919,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
#endif
if (orig->cpus_ptr == &orig->cpus_mask)
tsk->cpus_ptr = &tsk->cpus_mask;
+ dup_user_cpus_ptr(tsk, orig, node);

/*
* One for the user space visible state that goes away when reaped.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8ca7854747f1..9349b8ecbcf9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2124,6 +2124,26 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
__do_set_cpus_allowed(p, new_mask, 0);
}

+int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
+ int node)
+{
+ if (!src->user_cpus_ptr)
+ return 0;
+
+ dst->user_cpus_ptr = kmalloc_node(cpumask_size(), GFP_KERNEL, node);
+ if (!dst->user_cpus_ptr)
+ return -ENOMEM;
+
+ cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr);
+ return 0;
+}
+
+void release_user_cpus_ptr(struct task_struct *p)
+{
+ kfree(p->user_cpus_ptr);
+ p->user_cpus_ptr = NULL;
+}
+
/*
* This function is wildly self concurrent; here be dragons.
*
--
2.31.1.818.g46aad6cb9e-goog