mm_release() call in exit_mm() looks dangerous

["Jesper Juhl" <jesper.juhl@gmail.com>]

In kernel/exit.c we have this code :

static void exit_mm(struct task_struct * tsk)
{
        struct mm_struct *mm = tsk->mm;

        mm_release(tsk, mm);
        if (!mm)
                return;
...


But, mm_release() may dereference it's second argument ('mm'), so
shouldn't we be doing the "!mm" test *before* we call mm_release() and
not after?
I don't know the mm code well enough to be able to tell if some of the
other stuff mm_release does needs to be done always and the mm
dereference can't actually happen, but maybe someone else who knows
the code better can tell...  In any case, what's currently there looks
a little shaky..

-- 
Jesper Juhl <jesper.juhl@gmail.com>
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