[PATCH v2] pids: introduce find_get_task_by_vpid helper

[PATCH v2] pids: introduce find_get_task_by_vpid helper

[Mike Rapoport]

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

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
---

v2: remove  futex_find_get_task() and ptrace_get_task_struct() as Oleg
suggested

 include/linux/sched.h  |  5 +++++
 kernel/futex.c         | 20 +-------------------
 kernel/pid.c           | 13 +++++++++++++
 kernel/ptrace.c        | 27 ++++++---------------------
 kernel/taskstats.c     |  6 +-----
 mm/process_vm_access.c |  6 +-----
 6 files changed, 27 insertions(+), 50 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 26a7df4e558c..4c3af5255fcf 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1484,6 +1484,11 @@ 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 0518a0bfc746..e2a160549a0c 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
 
 /*
@@ -1166,7 +1148,7 @@ 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 020dedbdf066..ead086b0ef8e 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -462,6 +462,19 @@ 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 84b1367935e4..6f3de14313f5 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -1099,21 +1099,6 @@ 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
@@ -1131,9 +1116,9 @@ 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;
 	}
 
@@ -1278,9 +1263,9 @@ 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;
-- 
2.7.4

Re: [PATCH v2] pids: introduce find_get_task_by_vpid helper

[Balbir Singh]

On Sat, Oct 28, 2017 at 4:52 AM, Mike Rapoport <rppt@linux.vnet.ibm.com> wrote:
> There are several functions that do find_task_by_vpid() followed by
> get_task_struct(). We can use a helper function instead.
>
> Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
> ---

I did a quick grep and found other similar patterns in
kernel/events/core.c, kernel/kcmp.c
kernel/sys.c , kernel/time/posix-cpu-timers.c,
arch/x86/kernel/cpu/intel_rdt_rdtgroup.c,
security/yama/yama_lsm.c, mm/process_vm_access.c, mm/mempolicy.c and
arch/ia64/kernel/perfmon.c


Balbir Singh.

Re: [PATCH v2] pids: introduce find_get_task_by_vpid helper

[Mike Rapoport]

On Mon, Oct 30, 2017 at 07:51:42PM +1100, Balbir Singh wrote:
> On Sat, Oct 28, 2017 at 4:52 AM, Mike Rapoport <rppt@linux.vnet.ibm.com> wrote:
> > There are several functions that do find_task_by_vpid() followed by
> > get_task_struct(). We can use a helper function instead.
> >
> > Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
> > ---
> 
> I did a quick grep and found other similar patterns in

(reordered the file list a bit)

> kernel/events/core.c,
> arch/x86/kernel/cpu/intel_rdt_rdtgroup.c,
> mm/mempolicy.c,

Those and mm/migrate.c indeed have a similar pattern, but they all do

	task = pid ? find_task_by_vpid(pid) : current;

And I don't see an elegant way to use find_get_task_by_vpid() in this case.

> kernel/kcmp.c,

kcmp gets both tasks between rcu_read_lock/unlock and I think it's better
to keep it this way.

> kernel/sys.c,

There is no get_task_struct() after find_task_by_vpid(), unless I've missed
something

> kernel/time/posix-cpu-timers.c,

Here the task is selected with more complex logic than just
find_task_by_vpid() 

> mm/process_vm_access.c,

Converted in the patch

> security/yama/yama_lsm.c,
> arch/ia64/kernel/perfmon.c

I've missed these two, indeed.

The arch/ia64/kernel/perfmon.c even still uses read_lock(&tasklist) rather
than rcu_read_lock()...
 
> Balbir Singh.
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH v2] pids: introduce find_get_task_by_vpid helper

[Oleg Nesterov]

On 10/27, Mike Rapoport wrote:
>
> There are several functions that do find_task_by_vpid() followed by
> get_task_struct(). We can use a helper function instead.
>
> Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
> ---
>
> v2: remove  futex_find_get_task() and ptrace_get_task_struct() as Oleg
> suggested

Acked-by: Oleg Nesterov <oleg@redhat.com>