umd: Remove exit_umh

The bpfilter code no longer uses the umd_info.cleanup callback.  This
callback is what exit_umh exists to call.  So remove exit_umh and all
of it's associated booking.

v1: https://lkml.kernel.org/r/87bll6dlte.fsf_-_@x220.int.ebiederm.org
v2: https://lkml.kernel.org/r/87y2o53abg.fsf_-_@x220.int.ebiederm.org
Link: https://lkml.kernel.org/r/20200702164140.4468-15-ebiederm@xmission.comReviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

include/linux/sched.h

@@ -1511,7 +1511,6 @@ extern struct pid *cad_pid;
 #define PF_KTHREAD		0x00200000	/* I am a kernel thread */
 #define PF_RANDOMIZE		0x00400000	/* Randomize virtual address space */
 #define PF_SWAPWRITE		0x00800000	/* Allowed to write to swap */
-#define PF_UMH			0x02000000	/* I'm an Usermodehelper process */
 #define PF_NO_SETAFFINITY	0x04000000	/* Userland is not allowed to meddle with cpus_mask */
 #define PF_MCE_EARLY		0x08000000      /* Early kill for mce process policy */
 #define PF_MEMALLOC_NOCMA	0x10000000	/* All allocation request will have _GFP_MOVABLE cleared */

include/linux/usermode_driver.h

@@ -4,26 +4,10 @@
 #include <linux/umh.h>
 #include <linux/path.h>
 
-#ifdef CONFIG_BPFILTER
-void __exit_umh(struct task_struct *tsk);
-
-static inline void exit_umh(struct task_struct *tsk)
-{
-	if (unlikely(tsk->flags & PF_UMH))
-		__exit_umh(tsk);
-}
-#else
-static inline void exit_umh(struct task_struct *tsk)
-{
-}
-#endif
-
 struct umd_info {
 	const char *driver_name;
 	struct file *pipe_to_umh;
 	struct file *pipe_from_umh;
-	struct list_head list;
-	void (*cleanup)(struct umd_info *info);
 	struct path wd;
 	struct pid *tgid;
 };

kernel/exit.c

@@ -63,7 +63,6 @@
 #include <linux/random.h>
 #include <linux/rcuwait.h>
 #include <linux/compat.h>
-#include <linux/usermode_driver.h>
 
 #include <linux/uaccess.h>
 #include <asm/unistd.h>
@@ -805,8 +804,6 @@ void __noreturn do_exit(long code)
 	exit_task_namespaces(tsk);
 	exit_task_work(tsk);
 	exit_thread(tsk);
-	if (group_dead)
-		exit_umh(tsk);
 
 	/*
 	 * Flush inherited counters to the parent - before the parent

kernel/usermode_driver.c

@@ -9,9 +9,6 @@
 #include <linux/task_work.h>
 #include <linux/usermode_driver.h>
 
-static LIST_HEAD(umh_list);
-static DEFINE_MUTEX(umh_list_lock);
-
 static struct vfsmount *blob_to_mnt(const void *data, size_t len, const char *name)
 {
 	struct file_system_type *type;
@@ -134,7 +131,6 @@ static int umd_setup(struct subprocess_info *info, struct cred *new)
 	umd_info->pipe_to_umh = to_umh[1];
 	umd_info->pipe_from_umh = from_umh[0];
 	umd_info->tgid = get_pid(task_tgid(current));
-	current->flags |= PF_UMH;
 	return 0;
 }
 
@@ -182,11 +178,6 @@ int fork_usermode_driver(struct umd_info *info)
 		goto out;
 
 	err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
-	if (!err) {
-		mutex_lock(&umh_list_lock);
-		list_add(&info->list, &umh_list);
-		mutex_unlock(&umh_list_lock);
-	}
 out:
 	if (argv)
 		argv_free(argv);
@@ -194,23 +185,4 @@ int fork_usermode_driver(struct umd_info *info)
 }
 EXPORT_SYMBOL_GPL(fork_usermode_driver);
 
-void __exit_umh(struct task_struct *tsk)
-{
-	struct umd_info *info;
-	struct pid *tgid = task_tgid(tsk);
-
-	mutex_lock(&umh_list_lock);
-	list_for_each_entry(info, &umh_list, list) {
-		if (info->tgid == tgid) {
-			list_del(&info->list);
-			mutex_unlock(&umh_list_lock);
-			goto out;
-		}
-	}
-	mutex_unlock(&umh_list_lock);
-	return;
-out:
-	if (info->cleanup)
-		info->cleanup(info);
-}