pids: introduce find_get_task_by_vpid() helper

There are several functions that do find_task_by_vpid() followed by
get_task_struct().  We can use a helper function instead.

Link: http://lkml.kernel.org/r/1509602027-11337-1-git-send-email-rppt@linux.vnet.ibm.com
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/ia64/kernel/perfmon.c

@@ -2610,17 +2610,10 @@ pfm_get_task(pfm_context_t *ctx, pid_t pid, struct task_struct **task)
 	if (pid < 2) return -EPERM;
 
 	if (pid != task_pid_vnr(current)) {
-
-		read_lock(&tasklist_lock);
-
-		p = find_task_by_vpid(pid);
-
 		/* make sure task cannot go away while we operate on it */
-		if (p) get_task_struct(p);
-
-		read_unlock(&tasklist_lock);
-
-		if (p == NULL) return -ESRCH;
+		p = find_get_task_by_vpid(pid);
+		if (!p)
+			return -ESRCH;
 	}
 
 	ret = pfm_task_incompatible(ctx, p);

include/linux/sched.h

@@ -1489,6 +1489,11 @@ static inline struct thread_info *task_thread_info(struct task_struct *task)
 extern struct task_struct *find_task_by_vpid(pid_t nr);
 extern struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns);
 
+/*
+ * find a task by its virtual pid and get the task struct
+ */
+extern struct task_struct *find_get_task_by_vpid(pid_t nr);
+
 extern int wake_up_state(struct task_struct *tsk, unsigned int state);
 extern int wake_up_process(struct task_struct *tsk);
 extern void wake_up_new_task(struct task_struct *tsk);

kernel/futex.c

@@ -862,24 +862,6 @@ static void put_pi_state(struct futex_pi_state *pi_state)
 	}
 }
 
-/*
- * Look up the task based on what TID userspace gave us.
- * We dont trust it.
- */
-static struct task_struct *futex_find_get_task(pid_t pid)
-{
-	struct task_struct *p;
-
-	rcu_read_lock();
-	p = find_task_by_vpid(pid);
-	if (p)
-		get_task_struct(p);
-
-	rcu_read_unlock();
-
-	return p;
-}
-
 #ifdef CONFIG_FUTEX_PI
 
 /*
@@ -1183,7 +1165,7 @@ static int attach_to_pi_owner(u32 uval, union futex_key *key,
 	 */
 	if (!pid)
 		return -ESRCH;
-	p = futex_find_get_task(pid);
+	p = find_get_task_by_vpid(pid);
 	if (!p)
 		return -ESRCH;
 

kernel/pid.c

@@ -343,6 +343,19 @@ struct task_struct *find_task_by_vpid(pid_t vnr)
 	return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
 }
 
+struct task_struct *find_get_task_by_vpid(pid_t nr)
+{
+	struct task_struct *task;
+
+	rcu_read_lock();
+	task = find_task_by_vpid(nr);
+	if (task)
+		get_task_struct(task);
+	rcu_read_unlock();
+
+	return task;
+}
+
 struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
 {
 	struct pid *pid;

kernel/ptrace.c

@@ -1103,21 +1103,6 @@ int ptrace_request(struct task_struct *child, long request,
 	return ret;
 }
 
-static struct task_struct *ptrace_get_task_struct(pid_t pid)
-{
-	struct task_struct *child;
-
-	rcu_read_lock();
-	child = find_task_by_vpid(pid);
-	if (child)
-		get_task_struct(child);
-	rcu_read_unlock();
-
-	if (!child)
-		return ERR_PTR(-ESRCH);
-	return child;
-}
-
 #ifndef arch_ptrace_attach
 #define arch_ptrace_attach(child)	do { } while (0)
 #endif
@@ -1135,9 +1120,9 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
 		goto out;
 	}
 
-	child = ptrace_get_task_struct(pid);
-	if (IS_ERR(child)) {
-		ret = PTR_ERR(child);
+	child = find_get_task_by_vpid(pid);
+	if (!child) {
+		ret = -ESRCH;
 		goto out;
 	}
 
@@ -1281,9 +1266,9 @@ COMPAT_SYSCALL_DEFINE4(ptrace, compat_long_t, request, compat_long_t, pid,
 		goto out;
 	}
 
-	child = ptrace_get_task_struct(pid);
-	if (IS_ERR(child)) {
-		ret = PTR_ERR(child);
+	child = find_get_task_by_vpid(pid);
+	if (!child) {
+		ret = -ESRCH;
 		goto out;
 	}
 

kernel/taskstats.c

@@ -194,11 +194,7 @@ static int fill_stats_for_pid(pid_t pid, struct taskstats *stats)
 {
 	struct task_struct *tsk;
 
-	rcu_read_lock();
-	tsk = find_task_by_vpid(pid);
-	if (tsk)
-		get_task_struct(tsk);
-	rcu_read_unlock();
+	tsk = find_get_task_by_vpid(pid);
 	if (!tsk)
 		return -ESRCH;
 	fill_stats(current_user_ns(), task_active_pid_ns(current), tsk, stats);

mm/process_vm_access.c

@@ -197,11 +197,7 @@ static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 	}
 
 	/* Get process information */
-	rcu_read_lock();
-	task = find_task_by_vpid(pid);
-	if (task)
-		get_task_struct(task);
-	rcu_read_unlock();
+	task = find_get_task_by_vpid(pid);
 	if (!task) {
 		rc = -ESRCH;
 		goto free_proc_pages;

security/yama/yama_lsm.c

@@ -250,15 +250,10 @@ int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
 		} else {
 			struct task_struct *tracer;
 
-			rcu_read_lock();
-			tracer = find_task_by_vpid(arg2);
-			if (tracer)
-				get_task_struct(tracer);
-			else
+			tracer = find_get_task_by_vpid(arg2);
+			if (!tracer) {
 				rc = -EINVAL;
-			rcu_read_unlock();
-
-			if (tracer) {
+			} else {
 				rc = yama_ptracer_add(tracer, myself);
 				put_task_struct(tracer);
 			}