task_work: Revert "hold task_lock around checks in keyctl"

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() now fails if it is called
after exit_task_work().

Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20120826191214.GA4231@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 3364fbf..6cfc647 100644 (file)
--- 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)