pid: sprinkle tasklist_lock asserts

They cost nothing on production kernels and document the requirement of
holding the tasklist_lock lock in respective routines.

Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/r/20250206164415.450051-4-mjguzik@gmail.com
Acked-by: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/kernel/pid.c b/kernel/pid.c
index 924084713be8ba9883b379baa346703fc1c91aff..2ae872f689a758b1ddad22a93583fe1b6ee34d24 100644 (file)
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -339,17 +339,23 @@ static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type)
  */
 void attach_pid(struct task_struct *task, enum pid_type type)
 {
-       struct pid *pid = *task_pid_ptr(task, type);
+       struct pid *pid;
+
+       lockdep_assert_held_write(&tasklist_lock);
+
+       pid = *task_pid_ptr(task, type);
        hlist_add_head_rcu(&task->pid_links[type], &pid->tasks[type]);
 }
 
 static void __change_pid(struct task_struct *task, enum pid_type type,
                        struct pid *new)
 {
-       struct pid **pid_ptr = task_pid_ptr(task, type);
-       struct pid *pid;
+       struct pid **pid_ptr, *pid;
        int tmp;
 
+       lockdep_assert_held_write(&tasklist_lock);
+
+       pid_ptr = task_pid_ptr(task, type);
        pid = *pid_ptr;
 
        hlist_del_rcu(&task->pid_links[type]);
@@ -386,6 +392,8 @@ void exchange_tids(struct task_struct *left, struct task_struct *right)
        struct hlist_head *head1 = &pid1->tasks[PIDTYPE_PID];
        struct hlist_head *head2 = &pid2->tasks[PIDTYPE_PID];
 
+       lockdep_assert_held_write(&tasklist_lock);
+
        /* Swap the single entry tid lists */
        hlists_swap_heads_rcu(head1, head2);
 
@@ -403,6 +411,7 @@ void transfer_pid(struct task_struct *old, struct task_struct *new,
                           enum pid_type type)
 {
        WARN_ON_ONCE(type == PIDTYPE_PID);
+       lockdep_assert_held_write(&tasklist_lock);
        hlist_replace_rcu(&old->pid_links[type], &new->pid_links[type]);
 }