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Subject[PATCH] posix-cpu-timers: rcu_read_lock/unlock protect find_task_by_vpid call
Commit 4221a9918e38b7494cee341dda7b7b4bb8c04bde "Add RCU check for
find_task_by_vpid()" introduced rcu_lockdep_assert to find_task_by_pid_ns.
Add rcu_read_lock/rcu_read_unlock to call find_task_by_vpid.

Tetsuo Handa wrote:

Quoting from one of posts in that thead
http://kerneltrap.org/mailarchive/linux-kernel/2010/2/8/4536388

| Usually tasklist gives enough protection, but if copy_process() fails
| it calls free_pid() lockless and does call_rcu(delayed_put_pid().
| This means, without rcu lock find_pid_ns() can't scan the hash table
| safely.


Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

---

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 6842eeb..855bc53 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -38,11 +38,13 @@ static int check_clock(const clockid_t which_clock)
return 0;

read_lock(&tasklist_lock);
+ rcu_read_lock();
p = find_task_by_vpid(pid);
if (!p || !(CPUCLOCK_PERTHREAD(which_clock) ?
same_thread_group(p, current) : thread_group_leader(p))) {
error = -EINVAL;
}
+ rcu_read_unlock();
read_unlock(&tasklist_lock);

return error;
@@ -395,17 +397,21 @@ int posix_cpu_timer_create(struct k_itimer *new_timer)
if (pid == 0) {
p = current;
} else {
+ rcu_read_lock();
p = find_task_by_vpid(pid);
if (p && !same_thread_group(p, current))
p = NULL;
+ rcu_read_unlock();
}
} else {
if (pid == 0) {
p = current->group_leader;
} else {
+ rcu_read_lock();
p = find_task_by_vpid(pid);
if (p && !thread_group_leader(p))
p = NULL;
+ rcu_read_unlock();
}
}
new_timer->it.cpu.task = p;


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