This reverts commit d35abdb28824cf74f0a106a0f9c6f3ff700a35bf.

task_lock() was added to ensure exit_mm() and thus exit_task_work() is
not possible before task_work_add().

This is wrong, task_lock() must not be nested with write_lock(tasklist).
And this is no longer needed, task_work_add() fails if it is called
after exit_task_work().

Reported-by: Dave Jones <da...@redhat.com>
Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
 security/keys/keyctl.c |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 3364fbf..6cfc647 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1486,7 +1486,6 @@ long keyctl_session_to_parent(void)
        oldwork = NULL;
        parent = me->real_parent;
 
-       task_lock(parent);
        /* the parent mustn't be init and mustn't be a kernel thread */
        if (parent->pid <= 1 || !parent->mm)
                goto unlock;
@@ -1530,7 +1529,6 @@ long keyctl_session_to_parent(void)
        if (!ret)
                newwork = NULL;
 unlock:
-       task_unlock(parent);
        write_unlock_irq(&tasklist_lock);
        rcu_read_unlock();
        if (oldwork)
-- 
1.5.5.1

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