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    SubjectRe: [PATCH] ftrace: Avoid double-free of dyn_ftrace
    On Wed, Mar 25, 2009 at 10:25:47AM +0800, Zhaolei wrote:
    > >> >
    > >> > I'm wondering, did you trigger this in practice (if yes, how?),
    > >> > or have you found it via code review?
    > >> Hello, Ingo
    > >>
    > >> It is found via code review.
    > >
    > > Hmm, could you explain this more. I'm thinking that this scenario should
    > > not happen, and if it does, it should probably be a bug.
    > >
    > > Because when we call ftrace_free_rec we change the rec->ip to point to the
    > > next record in the chain. Something is very wrong if rec->ip >= s &&
    > > rec->ip < e and the record is already free.
    > Hello, Steven
    >
    > Thanks for your comment.
    > I got your meaning, and I agree that if rec->ip >= s && rec->ip < e,
    > this record is not freed.
    > But IMHO, "if rec->ip >= s && rec->ip < e" is used to select records in the module,
    > and function of ignore "freed record" is only its side-effect.
    > So, add a special judgement to avoid "freed record" is not a bad idea.
    > And I also agree your suggestion of add a WARN_ON, because this should not happened.

    Hi Zhaolei,

    Great! Feel free to send another patch ;-)

    Note, use FTRACE_WARN_ON() macro. This way it shuts down ftrace if it is hit and
    helps to avoid further damage later.

    -- Steve



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