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>

8 files changed, 33 insertions, 68 deletions

diff --git a/arch/ia64/kernel/perfmon.c b/arch/ia64/kernel/perfmon.c
index c44f002e8f6b..858602494096 100644
--- a/arch/ia64/kernel/perfmon.c
+++ b/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);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 166144c04ef6..ce5a27304b03 100644
--- a/include/linux/sched.h
+++ b/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);
diff --git a/kernel/futex.c b/kernel/futex.c
index 7f719d110908..1f450e092c74 100644
--- a/kernel/futex.c
+++ b/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;
 
diff --git a/kernel/pid.c b/kernel/pid.c
index 5d30c87e3c42..ed6c343fe50d 100644
--- a/kernel/pid.c
+++ b/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;
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 5e1d713c8e61..21fec73d45d4 100644
--- a/kernel/ptrace.c
+++ b/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;
         }
 
diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index 4559e914452b..4e62a4a8fa91 100644
--- a/kernel/taskstats.c
+++ b/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);
diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
index 8973cd231ece..16424b9ae424 100644
--- a/mm/process_vm_access.c
+++ b/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;
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index 8298e094f4f7..ffda91a4a1aa 100644
--- a/security/yama/yama_lsm.c
+++ b/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);
                         }