[Devel] [PATCH 12/12] Deprecate the find_task_by_pid

[Pavel Emelyanov]

There are some places that are known to operate on tasks'
global pids only:

* the rest_init() call (called on boot)
* the kgdb's getthread
* the create_kthread() (since the kthread is run in init ns)

So use the find_task_by_pid_ns(..., &init_pid_ns) there
and schedule the find_task_by_pid for removal.

Signed-off-by: Pavel Emelyanov <xemul at openvz.org>

---
 Documentation/feature-removal-schedule.txt |   19 +++++++++++++++++++
 include/linux/sched.h                      |    2 +-
 init/main.c                                |    2 +-
 kernel/kgdb.c                              |    2 +-
 kernel/kthread.c                           |    2 +-
 5 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index be6c2db..1e6960d 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/Documentation/feature-removal-schedule.txt
@@ -264,3 +264,22 @@ Why:	These drivers are superseded by i810fb, intelfb and savagefb.
 Who:	Jean Delvare <khali at linux-fr.org>
 
 ---------------------------
+
+What:	find_task_by_pid
+When:	2.6.26
+Why:	With pid namespaces, calling this funciton will return the
+	wrong task when called from inside a namespace.
+
+	The best way to save a task pid and find a task by this
+	pid later, is to find this task's struct pid pointer (or get
+	it directly from the task) and call pid_task() later.
+
+	If someone really needs to get a task by its pid_t, then
+	he most likely needs the find_task_by_vpid() to get the
+	task from the same namespace as the current task is in, but
+	this may be not so in general.
+
+Who:	Pavel Emelyanov <xemul at openvz.org>
+
+---------------------------
+
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 198659b..ccb9bba 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1617,7 +1617,7 @@ extern struct pid_namespace init_pid_ns;
 extern struct task_struct *find_task_by_pid_type_ns(int type, int pid,
 		struct pid_namespace *ns);
 
-extern struct task_struct *find_task_by_pid(pid_t nr);
+extern struct task_struct *find_task_by_pid(pid_t nr) __deprecated;
 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);
diff --git a/init/main.c b/init/main.c
index e702632..38a16ba 100644
--- a/init/main.c
+++ b/init/main.c
@@ -437,7 +437,7 @@ static void noinline __init_refok rest_init(void)
 	kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
 	numa_default_policy();
 	pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
-	kthreadd_task = find_task_by_pid(pid);
+	kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
 	unlock_kernel();
 
 	/*
diff --git a/kernel/kgdb.c b/kernel/kgdb.c
index 87b0463..6de0fd0 100644
--- a/kernel/kgdb.c
+++ b/kernel/kgdb.c
@@ -621,7 +621,7 @@ static struct task_struct *getthread(struct pt_regs *regs, int tid)
 	if (!tid)
 		return NULL;
 
-	return find_task_by_pid(tid);
+	return find_task_by_pid_ns(tid, &init_pid_ns);
 }
 
 #ifdef CONFIG_SMP
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 0ac8878..b9caa46 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -99,7 +99,7 @@ static void create_kthread(struct kthread_create_info *create)
 		struct sched_param param = { .sched_priority = 0 };
 		wait_for_completion(&create->started);
 		read_lock(&tasklist_lock);
-		create->result = find_task_by_pid(pid);
+		create->result = find_task_by_pid_ns(pid, &init_pid_ns);
 		read_unlock(&tasklist_lock);
 		/*
 		 * root may have changed our (kthreadd's) priority or CPU mask.
-- 
1.5.3.4