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    SubjectRe: [PATCH 1/4] pid_ns: zap_pid_ns_processes: fix the ->child_reaper changing
    On 08/26, Serge E. Hallyn wrote:
    >
    > Quoting Oleg Nesterov (oleg@tv-sign.ru):
    > > zap_pid_ns_processes() sets pid_ns->child_reaper = NULL, this is wrong.
    > > ...
    > > Even if there are no childs, it is not good that forget_original_parent()
    > > uses reaper == NULL.
    > > ...
    >
    > Well while it looked correct to me all along, I couldn't get the
    > testcase to cause an oops.

    Perhaps you can start several instances or increase the delay, I
    forgot that usleep() uses usecs, not msecs. In any case I agree,
    the test-case is oversimplified, but since it worked for me I didn't
    try to make it more "stubborn".

    > Acked-by: Serge Hallyn <serue@us.ibm.com>

    Thanks!

    > > + /*
    > > + * We can not clear ->child_reaper or leave it alone.
    > > + * There may by stealth EXIT_DEAD tasks on ->children,
    > > + * forget_original_parent() must move them somewhere.
    >
    > Actually this comment is a little bit misleading - the null
    > deref will happen regardless of whether there are children,
    > right?

    Yes, the comment could be better ;)

    But no, we won't oops without children. Please note that
    forget_original_parent() uses reaper inside the
    list_for_each_entry_safe(father->children) loop. ->children is
    empty, reaper is not used at all.

    But please also note the "not good" part of the changelog above.


    Thanks to all for review!

    Oleg.



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