sysctl: add procfs interface to disable/enable usermodhelper_affinity

hulk inclusion
category: feature
feature: performance/latency
upstream: never
bugzilla: 2680,10641
CVE: NA

The pervious patch "kmod: run usermodehelpers only on cpus allowed for
kthreadd V2" allow to set usermodehelper thread's affinity.

add a interface to disable/enable usermodhelper_affinity.
Disabled by default.

[XQ: backport patch from euleros 2.x:
  - kmod.c => umh.c
]
Signed-off-by: NXie XiuQi <xiexiuqi@huawei.com>
Reviewed-by: NLi Bin <huawei.libin@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

include/linux/sched/sysctl.h

@@ -83,4 +83,5 @@ extern int sysctl_schedstats(struct ctl_table *table, int write,
 				 void __user *buffer, size_t *lenp,
 				 loff_t *ppos);
 
+extern int sysctl_umh_affinity;
 #endif /* _LINUX_SCHED_SYSCTL_H */

kernel/sysctl.c

@@ -1240,6 +1240,15 @@ static struct ctl_table kern_table[] = {
 		.extra2		= &one,
 	},
 #endif
+	{
+		.procname	= "usermodhelper_affinity",
+		.data		= &sysctl_umh_affinity,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &zero,
+		.extra2		= &one,
+	},
 	{ }
 };
 

kernel/umh.c

@@ -28,6 +28,7 @@
 #include <linux/shmem_fs.h>
 #include <linux/pipe_fs_i.h>
 #include <linux/kthread.h>
+#include <linux/sched/sysctl.h>
 
 #include <trace/events/module.h>
 
@@ -39,6 +40,8 @@ static kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET;
 static DEFINE_SPINLOCK(umh_sysctl_lock);
 static DECLARE_RWSEM(umhelper_sem);
 
+int __read_mostly sysctl_umh_affinity;
+
 static void call_usermodehelper_freeinfo(struct subprocess_info *info)
 {
 	if (info->cleanup)
@@ -80,7 +83,10 @@ static int call_usermodehelper_exec_async(void *data)
 	 * start the usermode helper threads only on the processors allowed for
 	 * kthreadd.
 	 */
+	if (sysctl_umh_affinity)
 		set_kthreadd_affinity();
+	else
+		set_cpus_allowed_ptr(current, cpu_all_mask);
 
 	/*
 	 * Our parent (unbound workqueue) runs with elevated scheduling