[PATCH] futex_find_get_task(): don't take tasklist_lock

It is ok to do find_task_by_pid() + get_task_struct() under
rcu_read_lock(), we cand drop tasklist_lock.

Note that testing of ->exit_state is racy with or without tasklist anyway.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/kernel/futex.c b/kernel/futex.c
index 9d260e838cffdca6f951d6625626ab9d62f19d81..ca8ef11feb6586ce41a825f9c37b791028ed9024 100644 (file)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -389,7 +389,7 @@ static struct task_struct * futex_find_get_task(pid_t pid)
 {
        struct task_struct *p;
 
-       read_lock(&tasklist_lock);
+       rcu_read_lock();
        p = find_task_by_pid(pid);
        if (!p)
                goto out_unlock;
@@ -403,7 +403,7 @@ static struct task_struct * futex_find_get_task(pid_t pid)
        }
        get_task_struct(p);
 out_unlock:
-       read_unlock(&tasklist_lock);
+       rcu_read_unlock();
 
        return p;
 }