On Tue, 30 Oct 2012, Luigi Semenzato wrote:

For completeness, I would like to report that the page fault in
mm_release looks legitimate.  The fault happens near here:

if (unlikely(tsk->robust_list)) {
    exit_robust_list(tsk);
    tsk->robust_list = NULL;
}

and robust_list is a userspace structure.

This is the only place where the hang occurs when there are several 
threads in the exit path with PF_EXITING and it causes the oom killer to 
defer killing a process?  If that's the case, then a simple 
tsk->robust_list check would be sufficient to avoid deferring incorrectly.

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